WordWeb Online

1. Informal or slang term meaning insane, strange, eccentric or stupid
   "I think he's going dippy";
   - balmy [archaic], barmy, bats, batty, bonkers, buggy [N. Amer], cracked, crackers, daft, dotty, fruity, haywire, kooky, kookie, loco, loony, loopy, nuts, nutty, round the bend, around the bend, wacky, whacky, daffy, nutsy [N. Amer], potty [Brit], daft as a brush [Brit], round the twist [Brit], wacko, cuckoo
    
2. Guided by whim and fancy
   - flighty, flyaway, head-in-the-clouds, scatterbrained

Derived forms: dippiest, dippier

See also: frivolous, insane