Nuances of: ふっと、ふと、ひょっこり、 どっと、 さっさ、不意に、唐突、突然、急に and いきなり。

Question

I'm reading a beginner book and noticed that the author uses a lot of different words that translate to suddenly or abruptly which is interesting, so I have been trying to figure out the differences in between them.

I have included some words I looked up and their supposed nuances but I'm not 100% sure they are correct so confirmation would be appreciated.

ふっと,　?
ひょっこり,　?
どっと,　?
ふと,　Focuses on the aspect that something was unintentional
不意に、ふいに、?
さっさ,　?
唐突,　とうとつ,　Only of human behavior
突然,　とつぜん,　Spontaneously / Instantly
急に,　きゅうに,　Fast paced change of events. (no surprise element, not instant)
いきなり,　Immediately / Without Warning*

*: In the sense of immediately being/doing something with no intermediate, such as:
I got stuck on the first question. (No in-between step)
He jumped in the pool and immediately began drowning. (No in-between step)

If anyone can elaborate or confirm it would be much appreciated. ^_^

Edit: Added ふっと, 不意に,　ひょっこり,　どっと,　さっさ.

Answer 1

I hope someone else will elaborate this. My attempt is the following:

ふっと　is like onomatopoeia expression. Something appears or goes away as the breeze.e.g. You feel like start backpacking to somewhere with a whiff.

ふと　is used when something suddenly pops up into your head.e.g. your friends you haven't seen for some time.

不意に　is used when you are unprepared something suddenly coming. e.g you are called in your back.

唐突に　is used when a course of expected action is suddenly changed. e.g. your schedule is suddenly asked to change.

I think 急に and 突然　are interchangeable in most case.

急に　is often used with your subject feeling when something suddenly changes greatly. e.g. your height is suddenly getting taller.　

突然　is used when something changes for a very short time. e.g. It's suddenly raining cats and dogs.

I guess your interpretation of いきなり is correct.

Answer 2

I think that this is a very interesting question, and I will try to line out the results of what I found out in this answer.

I think that it is important that we first differentiate between what is onomatopoeia and what is still written or was originally derived from kanji. The former have more of a feeling-like explanation and the latter have some interpretation room. Lastly, I will cover the words on your list that do not immediately carry the meaning of abruptness or unexpectedness (i.e. words I feel should not be in this list). Note, not all words have clear distinctions there are overlaps between their use cases.

Disclaimer: I will mostly aggregate information and mostly trust my sources if I think they make sense (i.e. I do not require any academic degree behind claims). Additionally I will add personal opinion and disclaim this appropriately, so read with this in mind since I am no native. Furhermore, note that your (and my) list is not extensive with respect to words that you listed, but you probably listed most of the important ones already. Finally, do not forget that there are worlds between spoken and written Japanese, I will outline the things as researched and exemplified by written Japanese. For spoken Japanese the explanations of Kimi Tanaka are certainly enough.

Onomatopoeia

Let us first tackle the words that (probably) originate from a feeling with respect to the pronunciation. Some of the nuances in this section might be harder to understand, since this is mostly dependent on your feeling for the language.

• ひょっこり - the ひょ transmits a certain aloofness or lightness that is implicit in the pronunctiation. So a certain event came up in a ひょっと light way, without you expecting it. Let us consider some example sentences (all from here, emphasis theirs):

  [...]ひょっこり訪ねて来た小学時代の同級生[...] (太宰治「嘘」青空文庫)

  すると、八ヵ月目かにです、娘がひょっこり戻ってきました。(小林多喜二「疵」青空文庫)

  そこへ兄きがひょっこり帰って来た。(森鴎外「里芋の芽と不動の目」青空文庫)

  we see that the word is mostly associated to people or objects appearing unexpectedly on visiting terms, i.e. they just lightly come over without any pretext or anything (the lightness is important for nuance).

• ふっと - This word carries the notion of breeziness that Kimi Tanaka outlined in his answer and is also well explained here. It is used for things that suddenly disappear and appear without reason. Like the movement of air. Not many good example sentences exist, but consider those from here (emphasis mine)

  夜中にふっと目が覚める

  ふっと名案が浮かんだ

  ふっと見えなくなる (from here)

  I think it is apparent why ふっと fits well here.

Meanings stemming from 漢字

Let us now get to the words that can be rewritten in 漢字 and try to derive their nuance from the signs used and confirm our findings in example sentences. Note, that not all words have their meaning that are still in direct relation with the signs, in these cases I just leave out the explanation as it is purely historical and unrelated to the question.

• 不図{ふと} -　the second character is usually used to hint at a meaning like planning or thinking over something. Thus by extension it just is used in relation to something one doesn't particularly feel the need to think over and thus comes to mind without one expecting it. This is exactly the notion Kimi Tanaka explained

  ところが今朝は如何なる吉日か、私は不図四十年前に、金博士から聞いた疑問の民族の名を思い出したのであった。(海野十三, from here, emphasis mine)

  ふと灯りが消える (from here, emphasis mine)

  They are not events that come and go like a breeze, but also not events that you expected to happen anytime soon or ever.

• 不意{ふい}に - you probably already know 意 from 意味, 意識 or others. It always has this meaning of in mind or in general something connected to you being mentally prepared for something as expressed by Kimi Tanaka. Consider the following examples from here (emphasis theirs)

  それが今不意に目の前へ、日の光りを透かした雲のような、あるいは猫柳の花のような銀鼠の姿を現したのである。(芥川竜之介「お時儀」青空文庫)

  私が茶の間で夕刊を読んでいたら、不意にあなたのお名前が放送せられ、つづいてあなたのお声が。(太宰治「きりぎりす」青空文庫)

  Personally, I would say that there is a slight difference between 不意 and 不図 in that the former feels like the event that happened is more lightweight and the latter is a more important event. Like while I was reading the evening newspaper I suddenly heard your name read out on the radio (that is the example sentence for 不意). While the sudden turning off of the lights (as in the example sentence for 不図) is of more direct personal consequence. This might just be me, most people would probably use them interchangeably.

• 唐突{とうとつ} - the description from Kimi Tanaka is again mostly correct it seems, as is supported here and here. It is used when there was a certain flow to a speech or movement of an object which is suddenly interrupted and changed. I think this needs to be more or less active, so a light cannot 唐突に go dark as it can ふと go dark, even though it is a continuous action. Let's look at some examples from here (emphasis theirs):

  Ｍは唐突とこんなことを尋ねた。(芥川竜之介「海のほとり」青空文庫)

  爺は、彫刻のように堅くなったが、「あッはッはッ。」　唐突に笑出した。(泉鏡花「燈明之巻」青空文庫)

  This should be straightforward to get a feeling for.

• 突然{とつぜん} - this describes the unexpected starting of motion or flow of speech (i.e. in general some action). The difference to 唐突 is that this does not require that some flow is broken, but that a new one starts. The example given here illustrates this well: You would say a parked car 突然 dashes off, but wouldn't say 唐突, as it just starts movement. Let's again look at some examples of usage from here (emphasis theirs)

  誰か外へ来たと見えて、戸を叩く音が、突然荒々しく聞え始めました。 (芥川竜之介「アグニの神」青空文庫)

  それは女の姿がその明るい電灯の光を突然遮ったためだった。(梶井基次郎「ある崖上の感情」青空文庫)

  It shall be noted that I think that 突然 is the most widely used suddenly-word and that it probably is misused a lot if you want to go hard-core on the definitions and origins of the words.

• 急{きゅう}に - I fear I will disagree with Kimi Tanaka here (at least on the literary side). This answer explains really well how I feel about the difference between 急に and 突然. It basically says that 急に is used for more normal surprising things, like ''急に I have become hungry'' or ''急に I have gotten another appointment and need to leave''. On the other hand, 突然 is used for really surprising things like ''突然に it started raining men''. You cannot interchange those two words in these 3 examples. Some easy examples are given on the nlpt preparation site

  授業中に、急に眠くなりました。

• 行{い}き成{な}り - This is very close in meaning to 急に and 突然 and for all intents and purposes it is used interchangeably and Japanese people will not be able to tell you what the differences between them is. Apart from the one outlined above there is a research paper from Nagoya University researching exactly the difference of these three words. It's very detailed and giving examples for very detailed nuances. As this answer is already long enough, I am not going to paraphrase it into this answer here, but be my guest and read it through, it is interesting to see all the example sentences.

• 突如{とつじょ} - is very similar to the previous 3 but mostly literary (i.e. you will probably never hear this word in spoken Japanese). You cannot use it interchangeably though, as something like 突如の出来事 just sounds weird while 突然の出来事 is fine. In books you will mostly see it as 突如として, as documented here and here. Furthermore, one can argue that 突如 is more for encounters the narrator didn't expect but somebody prepared while 突然 can also be used for more random things like rain.

Examples that shouldn't be in the list (in my opinion)

• どっと - I think you meant とっとと which derives from 「疾疾と」（とくとくと） and means (as the characters indicate) something like quick.
• さっさと - This derives from 「颯々」（さつさつ and basically signifies the blowing of the wind (which makes さーさー sounds in the trees). So you use it to say somebody should hurry (like the wind). Both this and the previous word are similar, their difference being elucidated in the link and not subject of this question.

Okay, sorry for this long answer. I got carried away, if this is too much written text just tell me, I'll mend it as good as I can. I just want you to know that for most situations these nuances are not important in spoken Japanese. And the examples I gave you are from over 50 years ago mostly (mostly the big Japanese writers). Japanese people today think that Japanese is very old-fashioned. So don't go learning these nuances and words expecting everybody to understand them. Even in written Japanese these Nuances come fairly naturally, so don't worry too much.