daffy adj.

c. 1200, "mild, well-mannered," Old English gedæfte "gentle, becoming," from Proto-Germanic *gadaftjaz (source also of Old English daeftan "to put in order, arrange," gedafen "suitable;" Gothic gadaban "to be fit"), from *dab-, which has no certain IE etymology and is perhaps a substratum word.

Sense deteriorated to "dull, awkward, uncouth, boorish" (c. 1300), perhaps via the notion of "humble." Further evolution to "foolish, simple, stupid" (mid-15c.) and "crazy" (1530s) probably was influenced by analogy with daffe "halfwit, fool, idiot" (see daffy); the whole group probably has a common origin. For sense evolution, compare nice, silly. Related: Daftly; daftness.

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.