The Collaborative International Dictionary of English v.0.48:
Adnoun \Ad"noun`\, n. [Pref. ad- + noun.] (Gram.) An adjective, or attribute. [R.] --Coleridge. [1913 Webster]WordNet (r) 3.0 (2006):
adnoun n 1: an adjective used as a noun; "`meek' in `blessed are the meek' is an adnoun"