Adnoun: An adjective that functions as a noun. Examples:
land of the free
home of the brave
blessed are the meek
I discovered adnoun while using the Hint function in computer Scrabble. None dare call it cheating!
P.S. Read what linguist Arnold Zwicky has to say about noun-y adjectives in this Oct. 31 Language Log post. (He doesn't call them "adnouns.") In this excerpt, "NP" stands for "noun phrase":
Wise in "The wise talk because they have something to say" is NOT a noun; it's an adjective, in a NP (the wise) that has no overt noun head. This NP is an instance of an odd construction in English that licenses the + Adj as an NP with generic reference — most commonly as a generic plural referring to human beings, so that it can be roughly glossed as 'Adj people'. Other examples: the soap opera "The Bold and the Beautiful", the Robin Hood slogan "steal from the rich and give to the poor", and a headline from yesterday's New York Times (p. 1): The Decided Go In Droves To Vote Early.