Harebrained \Hare"brained`\ (h[^a]r"br[=a]nd`), a. Wild; giddy; volatile; heedless. "A mad hare-brained fellow." --North (Plutarch). [Written also hairbrained.]

[1913 Webster]

Source: The Collaborative International Dictionary of English v.0.48
 

22 Moby Thesaurus words for "hare-brained": airy, asinine, brainless, crackpot, fanciful, flighty, foolhardy, foolish, frivolous, giddy, heedless, improvident, inane, madcap, mindless, rash, reckless, scatterbrained, silly, visionary, wild, witless

Source: Moby Thesaurus II by Grady Ward, 1.0
 

73 Moby Thesaurus words for "harebrained": absurd, adventurous, arbitrary, audacious, balmy, bold, brainless, capricious, cranky, crazy, crotchety, daredevil, daring, death-defying, dizzy, empty-headed, fanciful, fantasied, fantastic, featherbrained, featherheaded, fire-eating, flaky, flighty, fluttery, foolhardy, forward, freakish, frivolous, gaga, giddy, giddy-brained, giddy-headed, giddy-pated, giddy-witted, harebrain, humorsome, insane, kinky, loony, madbrain, madbrained, madcap, maggoty, moody, motiveless, notional, petulant, potty, preposterous, presumptuous, quirky, rattlebrained, rattleheaded, rattlepated, scatterbrained, scramblebrained, shatterbrained, silly, skittish, temperamental, thoughtless, unreasonable, unrestrained, vagarious, vagrant, wacky, wanton, wayward, whimsical, wild, wild-ass, witless

Source: Moby Thesaurus II by Grady Ward, 1.0
 

harebrained adj : very foolish; "harebrained ideas"; "took insane risks behind the wheel"; "a completely mad scheme to build a bridge between two mountains" [syn: insane, mad]

Source: WordNet (r) 2.0
 

Hare'brained' \Hare"'brained`'\, a. Wild; giddy; volatile; heedless. ``A mad hare-brained fellow.'' --North (Plutarch). [Written also hairbrained.]

Source: Webster's Revised Unabridged Dictionary (1913)