Which one is grammatically correct: "wood door" or "wooden door"

Question

I have a grammar which says that:

The noun + noun structure is normally used to say what things are made of.

A few pairs of nouns and adjectives are used as modifiers with different meanings. Generally the noun simply names the material something is made of, while the adjective has a more metaphorical meaning.

• a gold watch - golden memories;
• a silk stocking - silken skin

I've also heard that the -en ending is used in a poetic sense. But when I looked up at my dictionary for the word wooden, it brought as an example wooden bench; even though wooden wasn't being used in a figurative nor in a poetic way. Furthermore, I don't know whether to use wood door or wooden door, meaning that the door is made of wood.

Answer 1

The preference as between wood and wooden varies in English writing depending on the noun being modified. This is perhaps most easily illustrated by looking at a series of Google Ngram charts that match different adjective-noun combinations. In the case of modifiers for the noun door, as the Ngram graph that fev's answer cites, the preference for "wooden door" (red line) over "wood door" (blue line) was remarkably stable for almost 200 years, but has shot up impressively since about 1980:

The plots for "wood floor" (green line) and "wooden floor" (yellow line), overlaid on fev's original Ngram chart, are somewhat less consistent and indicate a somewhat weaker preference for wooden over wood:

Even more inconsistent are the results for "wood frame" (navy blue line) versus "wooden frame" (purple line):

In this case, "wood frame" was actually more frequent in published writing for a couple of decades (roughly 1970–1990), although "wooden frame" has more recently reasserted itself and the incidence of "wood frame" has dropped off considerably. (I should acknowledge that "wood/wooden frame" often appears as a compound modifier for a following noun such as house, which sets it apart from "wood/wooden door" and "wood/wooden floor"; however, that difference in application doesn't seem to me to be critical to the choice between wood and wooden.)

A couple of things emerge in this series of Ngram charts. First, the frequency of the "wooden" forms has increased sharply in the case of door and floor and significantly in the case of frame over the past 40 years, while the frequency of the "wood" forms has increased impressively in the case of floor, grown modestly in the case of door, and dropped by more than half in the case of frame during the same period. This suggests that we have entered an era of increased preference for wooden over wood, at least with regard to these three pairs of terms.

Second, the current degree of preference for the wooden term over the wood one seems to depend to a great extent on the following noun. Of the six terms tracked in the third Ngram chart above, "wooden door" is the most frequent and "wood door" is the least frequent, indicating a very strong preference for the former. Both "wooden floor" and "wood floor" have enjoyed upswings in popularity in the past three decades, although the plot for "wooden floor" has risen more sharply. And the frequencies of "wooden frame" and "wood frame" have gone in opposite directions since 1980, from a state of rough equality to one in which "wooden frame" is more than twice as frequent (although "wood frame" is still more frequent than "wood door"). The Ngram plots for "wood fence" versus "wooden fence," "wood table" versus "wooden table," etc., show similar profiles, with the "wooden" form more frequent than the "wood" form, and with the frequency of the "wooden" form increasing markedly in recent decades.

I don't know why the movement toward "wooden" forms is occurring. It is true that wooden always either literally or figuratively means "made of wood" whereas wood sometimes means "made of wood" and sometimes means "made to act on wood" (as in the case of "wood saw" and "wood glue")—but there are few instances where any serious ambiguity might arise from using "wood [noun]." The only one I can think of is "wood carrier," which might mean a carrier made of wood or a carrier for transporting wood.

The areas where "wood [noun]" dominates "[wooden] noun" are those where the sense of the term is "[noun] composed of pieces of wood"—for example "wood pile," "wood fire," and "wood shavings." In none of those specific instances does the "wooden" form sound right to me. Sure enough, we get this set of Ngram plots for "wood pile" (blue line) versus "wooden pile" (red line), "wood fire" (green line) versus "wooden fire" (yellow line), and "wood shavings" (light blue line) versus "wooden shavings" (maroon line):

The upsurge in instances of "wooden pile" in the late nineteenth and early twentieth centuries appears to involve occurrences of "pile" in the sense of "slender column or pillar driven into the ground and used to bear a vertical load" rather than in the sense of "stack or rick [of logs]." The blips in frequency of "wooden fire" during roughly the same period seem related to instances of such longer phrases as "wooden fire-box," "wooden fire escape," and "wooden fire doors."

Answer 2

You can say wood door, but wooden door is so much more common, as you can see in this Ngram, that I wouldn't bother to use the former.

Both wood and wooden, when used as adjectives, can be said to be relatively interchangeable:

When used adjectivally to describe something made out of the material from a tree, “wood” and “wooden” mean the same thing (as in “wood shutters” or “wooden shutters”). (Grammarphobia)

The same site shows that sometimes, that extra syllable -en can be useful for rhythm:

Even when “wood” and “wooden” mean the same thing, we wouldn’t necessarily consider them interchangeable. The choice of one or the other often depends on rhythm, style, euphony, and so on. If they were switched in this passage, the iambic meter would be disrupted:

• Upon a wooden coffin we attend. (Shakespeare, King Henry VI, Part 1, believed written in 1591).

Note that wooden, being an adjective, is much more flexible than wood used attributively as a noun.

Wood floor is more common than wood door, but still less common than wooden floor.

In an interesting post, a moderator of the grammar exchange explains:

When you refer to the beams in an old house, you'd say the wooden beams, right? And to the doors of an old building: wooden doors. But if you were buying a new house and putting things in it, you'd probably say:

• We're putting in new wood doors – we don't like the old metal ones.

And,

• We're getting all new wood bookcases – we don't like the composition ones.

It feels like the old, established articles are wooden, but the new ones, the ones that you acquire that aren't antiques, can be wood.

So, as it is often the case, your choice of words also depends on context.

With gold/golden, some say the difference seems to be between coulour and material:

If the word is meant to indicate something actually made of the substance, then we would use gold. If, on the other hand, we're trying to convey something that resembles the colour of gold or an idyllic or ideal situation, then we would use golden. (source)

But if you look at dictionaries, it's not so straightforward to guess that. Your will find names like Gold Hair Dye, although golden would clearly be more appropriate. I find this Ngram1 and this Ngram2 quite helpful in knowing which nouns are used more commonly in collocation with golden and gold respectively.

Answer 3

With regard to "wood" and "wooden", part of the choice depends on whether the "woodiness" of the object is fundamental or incidental. The door is perhaps the best example:

I might say "Go down the hallway and then go through the wood door on your left" when giving instructions. The door is wood, but I'm just describing it, the same way I might say "green door".

On the other hand, I might say "On the front of the cathedral is a massive wooden door." In this case, "wooden" is a part of the image of the door -- it's more than just an incidental characteristic.

For a bench, one would generally say "wooden bench", since "wooden" is more fundamental to the nature of a bench than to a door. But "wood bench" might be used if, eg, there were two similar benches side-by-side, one metal, one wood, and you merely wanted to identify which.

I suspect that this difference applies to several other "-en" choices, though I haven't considered them very much.