I have come across several times reading Chinese that they repeat words twice and then again.
For an Instance what is the difference between 热闹 and 热热闹闹 ?
what is the grammar meaning when words get multiplied in that manner?
As a native Chinese speaker, I've never learned the AABB "grammar rule" from book. This means it's never considered as a kind of grammar rule at least in my student age.
But I don't agree with @gcd0318. There is difference between AB and AABB. In Chinese, repeating usually means emphasize the AB word, or to make the sentence sounds good to phonology.
e.g. 勤恳(diligent and conscientious) vs. 勤勤恳恳 Although they have the same mean, but use 勤勤恳恳 always make the audience feel that the speaker is highly applaud one's diligent and conscientious. Use 勤恳 doesn't have the strong emotional feeling.
Back to your example, 热热闹闹, it's the same as usage of 勤勤恳恳. It emphasize how bustling it is.
And see this great answer for usage of repeating words in Chinese.
As adj./adv., XXYY/XYXY has grammar different after all. But XXYY/XYXY could be used as (just AS, but they are not verb. Chinese, natively, has no concept of part of speech) verb, with different meaning. Meanwhile XY sometimes has no such usage.
– gcd0318 Mar 08 '16 at 03:00I do believe there is a differential meaning in multiplied words. One important meaning is that to repeat a word or phrase in the AABB manner is to impose a fictive duration upon AB. For example, we can speak 热闹一下,but not *热热闹闹一下 because 热热闹闹 denotes a duration reading that is incompatible with the perfect meaning expressed by '一下'.
XXYY (sometimes XYXY) has nothing special comparing to XY, just an oral style. But not all adj. or adv. have such usage
我看看一下is weird, you could say我看一下or我看看. Same for我坐坐一下.我坐坐看看一下is weird,坐and看couldn't be used together like this.我热热闹闹一下is weird, you could say我热闹热闹or我热闹一下...Hmm...Better to say我们热闹一下or我们热闹热闹. – Dec 14 '15 at 10:38