I have been reading grammar instructions on this website.

When I came across the bottom of the page, there was a quiz. In the quiz it was noted that the word oak in the following sentence is an adjective.

In the spring, red roses blossom in my cute small garden. The beautiful birds also sing in the big oak tree.

Why is oak an adjective in the sentence?

  • 2
    This question is not a duplicate, since it asks about a compound word. oak tree is a compound word and has its own entry in the OED. So do cough drop and cough medicine, but cough trouble is not recognized as a compound word.
    – user20792
    Dec 15, 2015 at 14:59
  • 1
    Though "oak" in "oak tree" is very often said to be an adjective this is highly imprecise grammar terminology. "Oak tree"is a compond noun of the type noun + noun with "tree" being the main element and "oak" the subelement. English grammar should have a special term for "oak". I never use "adjective" for nouns that are subelement of compound nouns as it is confusion of grammar terms. Adjective is a word class, but oak is an element of word formation and as such quite different from normal adjectives.
    – rogermue
    Dec 15, 2015 at 18:50
  • 1
    There is "a black bird" and "a blackbird". It is nonsense to say "black" is an adjective in both nouns. That is very imprecise grammar terminology and I would not recommend it. "Black" in blackbird has quite a different function from a normal adjective and a special term would be necessary.
    – rogermue
    Dec 16, 2015 at 6:56

4 Answers 4


I wouldn't call it an adjective, I'd call it a modifier. A modifier is:

a word or phrase that adds to the meaning of another word or phrase by giving more information about it

A Wikipedia article about modifiers explains that modifiers can be adjectives, prepositional phrases, or other nouns. For example, consider this sentence:

Some loud birds are chirping in the oak tree with the dead branch.

In that sentence:

  • loud is an adjective modifying the plural noun birds,
  • oak is a noun adjunct modifying the word tree, and
  • with the dead branch is a prepositional phrase acting as a post-modifier to the noun phrase oak tree.

The word oak is functioning a lot like an adjective – I mean, oak tree looks a lot like yellow car – but I don't think it's entirely correct to call it an adjective.

When parsing a sentence, it can be hard to tell the difference between a noun phrase (like oak tree) and an adjective-noun pair (like hot soup). We can check a dictionary to see if the word in question gets listed as an adjective in the dictionary. For example, a word like compound will have definitions listed a noun and as an adjective, because the word can be used either way. However, most of the dictionaries I checked only listed oak as a noun, so I'd be more inclined to view it as a noun phrase. That said, I wouldn't want to be too dogmatic about the matter.


Oak is not an adjective in this sentence.

The word oak tree is a compound word. This means a word that combines two or more words, but it has the lexical status of being a single word.

Oak tree has its own dictionary entry in the Oxford Dictionary (OED).

Oak tree has its own dictionary entry in the free dictionary.

Third, when you look up oak in the ODO the entry says "also oak tree", meaning this is a variant or that the two are synonyms.

Some compound words are spelled with a space between the two components and some are not; some are spelled with hyphen between the two components. Compound words sometimes start with a hyphenated spelling and after a while the hyphen gets dropped. Some words start as two words and then become so common that they become a compound word (example: Chinese food).

Other compound words that are nouns include

horse race
mind set
silk merchant
car factory
bank clerk
key position
Chinese food
emergency plan
Republican party
rowing boat
energy vampire
punctuality nut
zombie powder

Compound words are different from two words that are, say, an adjective and a noun. The difference can usually be heard in pronunciation.

Compare orange juice (juice squeezed from an orange) and orange juice (any juice that is orange in color). The first, like most compound words, is stressed on the first word and has a falling intonation. The second has a rising intonation on the first word. This distinction in pronunciation is true for the following two pairs, and many similar pairs:

Also key position (the position of a key) as a compound word versus key position (a position that is key or important).

A blackbird is different from a black bird, not only in spelling but in pronunication.

Most these examples are taken from the Concise Oxford Companion to the English Language and The Oxford Dictionary of English Grammar (2 ed.).

Not all collocations are considered compound words. Like most things in English, frequency of usage plays a part. Cough drop and cough medicine are compound nouns; cough trouble is not recognized as one by the OED.

  • 4
    I really like your orange juice example, but I'm not sure I'd call oak tree a compound word (at least, not in the same way I'd call doorknob a compound word). I've always been taught that a word is compounded when they are joined to form a single lexeme. So, I'd call bottleneck a compound word, but bottle cap a noun phrase – but I won't go so far as to assert there are no allowances for wiggle room. You've given me much to ponder. (Not my downvote, btw.)
    – J.R.
    Dec 14, 2015 at 20:50
  • 1
    @J.R. Everything in this answer was taken from sources other than me. Either the OED, which calls oak tree a compound word, to the other resources. Also John McWhorter. I did not add a single word to the list I include. Even ODO says also Oak tree when you look up Oak. The OP should be aware of this viewpoint...I didn't write it for my sake. ;)
    – user20792
    Dec 15, 2015 at 3:31
  • NES - Like I said, I liked your answer. Sure enough, the OED has a separate entry for oak tree, which says, plain as day, "Etymology: Formed within English, by compounding." When it comes to two-word compounds, I liked Lawrence's ice cream example, too.
    – J.R.
    Dec 15, 2015 at 10:03
  • plus, I'm not sure that the relationship between the two components of a compound word are agreed on by all linguists. So I'm not sure if descriptors as to what to call oak in oak tree necessarily conflict with this answer. But we don't pronounce oak tree like we do tall tree or blackbird like we do black bird.
    – user20792
    Dec 15, 2015 at 11:16
  • 2
    @NES +1 I disagree with McWhorter on that though. In Chinese food, both words take stress which indicates that Chinese food is a regular adjective + noun combination. The reason that the stress within the word Chi'nese is different from the stress in the word when modifying food is just because of stress shift. You'll notice that it will also change in 'Chinese' headgear. It's the same way that the stress in on the second syllable in four'teen but this shifts to the first in 'fourteen 'episodes. Or consider cham'pagne and 'champagne 'cocktail. Dec 15, 2015 at 15:48

" Oak" is a noun functioning as an attribute in "oak tree".Some people mix the function with parts of speech.

  • anyway it's functioning like an adjective? Dec 14, 2015 at 19:08

In English, many words can fill more than one function of speech (but of course, many are limited to only one function of speech).

Oak can be a noun or an adjective.

An adjective generally does the job of answering the question "What kind of X?".

While English adjectives can sometimes come after the noun, usually they come before, and adjectives answering "What kind of X" almost always come before the noun.

@NES provided an answer that talked about compound words. Compound words in English can be separated by nothing (e.g. flowerpot), a hyphen (e.g. full-fledged), or a space (e.g. ice cream).

In the case where they are separated by a space, one word is obviously technically a modifier, but combined they mean something different than the original two words. Continuing with the example of ice cream - while ice and cream are used to make ice cream, the end result is not really a type of ice or a type of cream. It's a new thing. You'll probably might occasionally see people spell it incorrectly as one word for this reason, icecream.

Whereas with oak tree - it's still a tree - oak is qualifying the type of tree, thus this isn't really a compound word.

  • I like this answer – except for the part about spelling ice cream as a single word. I don't generally see that, and I would recommend that learners avoid spelling ice cream as a single word without the space.
    – J.R.
    Dec 15, 2015 at 10:05
  • 1
    Oak tree has its own separate entry in the OED, where it is listed as a compound noun. 'Chinese' qualifies 'food' in 'Chinese food' but the latter is a compound noun. As wikipedia: compound, says The meaning of the compound may be similar to or different from the meanings of its components in isolation. None of this denies that the 'oak' in 'oak tree' is a noun by itself.
    – user20792
    Dec 15, 2015 at 14:39

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