WordNet (r) 3.0 (2006):

loopy
    adj 1: consisting of or covered with or having loops
    2: informal or slang terms for mentally irregular; "it used to
       drive my husband balmy" [syn: balmy, barmy, bats,
       batty, bonkers, buggy, cracked, crackers, daft,
       dotty, fruity, haywire, kooky, kookie, loco,
       loony, loopy, nuts, nutty, round the bend, around
       the bend, wacky, whacky]