1951, U.S. student slang, probably an alteration of 1940s slang nert "stupid or crazy person," itself an alteration of nut. The word turns up in a Dr. Seuss book from 1950 ("If I Ran the Zoo"), which may have contributed to its rise.
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.