1. (n.) A fall that breaks the neck.

2. (n.) A steep place endangering the neck.

3. (a.) Producing danger of a broken neck; as, breakneck speed.

abrupt accident-prone agile bluff bold breathless careless dangerous daredevil dashing desperate devil-may-care double-quick eagle-winged excessive expeditious express fast fleet flying furious galloping hair-trigger harum-scarum hasty headlong hell for leather hotheaded hurried hustling impetuous impulsive light of heel light-footed lively mad mercurial nimble nimble-footed overeager overenthusiastic overzealous panting plunging precipitant precipitate precipitous prompt quick quick as lightning quick as thought rapid rash reckless running sharp sheer slap-bang slapdash snappy spanking speedy steep sudden swift vertical wanton wild winged