breakneck

• POS: Adjective
• HYPHEN: break=neck

CIDE DICTIONARY

breakneck, n. 

•  A fall that breaks the neck.  [1913 Webster]
•  A steep place endangering the neck.  [1913 Webster]

breakneck, a. 

 Producing danger of a broken neck; as, breakneck speed.  [1913 Webster]

OXFORD DICTIONARY

breakneck, adj. (of speed) dangerously fast.

THESAURUS

breakneck

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

ROGET THESAURUS

breakneck

Rashness

N rashness, temerity, want of caution, imprudence, indiscretion, overconfidence, presumption, audacity, precipitancy, precipitation, impetuosity, levity, foolhardihood, foolhardiness, heedlessness, thoughtlessness, carelessness, desperation, Quixotism, knight-errantry, fire eating, gaming, gambling, blind bargain, leap in the dark, leap of faith, fool's paradise, too many eggs in one basket, desperado, rashling, madcap, daredevil, Hotspur, fire eater, bully, bravo, Hector, scapegrace, enfant perdu, Don Quixote, knight-errant, Icarus, adventurer, gambler, gamester, dynamitard, boomer, rash, incautious, indiscreet, imprudent, improvident, temerarious, uncalculating, heedless, careless, without ballast, heels over head, head over heels, giddy, wanton, reckless, wild, madcap, desperate, devil-may-care, hot-blooded, hotheaded, hotbrained, headlong, headstrong, breakneck, foolhardy, harebrained, precipitate, impulsive, overconfident, overweening, venturesome, venturous, adventurous, Quixotic, fire eating, cavalier, janty, jaunty, free and easy, off one's guard, post haste, a corps perdu, hand over head, tete baissee, headforemost, happen what may, come what may, neck or nothing, the devil being in one, non semper temeritas est felix, paucis temeritas est bono multis malo.