1530s, "frothing, covered with barm;" see barm + -y (2). Figurative sense of "excited, flighty, bubbling with excitement" is from c. 1600. Meaning "foolish" (1892) is probably an alteration of balmy (q.v.).
Old English beorma "yeast, leaven," also "head of a beer," from Proto-Germanic *bhermen- "yeast" (source also of Dutch berm, Middle Low German barm), from suffixed form of PIE root *bhreu- "to boil, bubble, effervesce, burn."
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).