batty(s = adj.all) around the bend, balmy, barmy, bats, bonkers, buggy, cracked, crackers, daft, dotty, fruity, haywire, kookie, kooky, loco, loony, loopy, nuts, nutty, round the bend, wacky, whacky - informal or slang terms for mentally irregular; "it used to drive my husband balmy"

1.  Belonging to, or resembling, a bat. Shak. [1913 Webster]

2.  Crazy; demented; loony; nuts; as, her constant gabbing is driving me batty. [PJC]

batty, adj. (battier, battiest) sl. crazy.

Derivative:
battily adv. battiness n.

Etymology:
BAT(2) + -Y(1)