Can a noun work as an adjective, and the adjective as a noun?

Question

# Hazel EyesI found the following paragraph in the [guycounseling.com blog article “Hazel Eyes: Learn Why People with Greenish Eye Color are Rare!”](https://guycounseling.com/hazel-eyes-everything-you-ever-wanted-to-know-about-them/), containing the two words ***“hazel eyes”***:> Hazel eyes are fascinating to gaze into. When you look at someone who has hazel eyes, you see colors that are completely different than other eye colors, such as crystal blue or emerald green.> —[Guy Counseling Site](https://guycounseling.com/hazel-eyes-everything-you-ever-wanted-to-know-about-them/)I also found some text on another site that says: > Her eyes are hazel.*Hazel* is a **noun** that denotes a colour; how can *hazel* modify the noun *eyes* if *hazel* is **also** a noun itself? Doesn’t a word always **have** to be an adjective to modify a noun? Isn’t that what “adjective” means ***by its very definition***: a word that modifies a noun? How can something modify a noun without being an adjective? Is that even possible?The [dictionary entry for *hazel*](https://en.oxforddictionaries.com/definition/hazel) I found on the online Oxford Living Dictionaries website doesn’t mention that *hazel* can ever be adjective; it mentions only that it is a noun:> ## hazel> ɴᴏᴜɴ> 1. A temperate shrub or small tree with broad leaves, bearing prominent male catkins in spring and round hard-shelled edible nuts in autumn.> ^{Genus *Corylus*, family Betulaceae: several species, in particular the common Eurasian hazel (*C. avellana*)}> 2. [*mass noun*] A reddish-brown or greenish-brown colour, especially of a person’s eyes.> [*as modifier*] ‘the laughing hazel eyes were serious now’> —[Oxford Living Dictionaries](https://en.oxforddictionaries.com/definition/hazel)How can this be grammatical?> Her eyes (*noun*) are hazel (*noun*)?And also, if you accept that a noun can work as an adjective, then, can adjective work as a noun?

Answer 1

When the dictionary mentions hazel as "A reddish-brown or greenish-brown colour" it is describing hazel as an adjective. I am not sure why the Oxford Living Dictionary described it as a "mass noun" when it meant adjective based on the definition provided.

No other words I know of can be both nouns and adjectives unless an adjective were to be used as a proper noun which is different from traditional nouns.