Synonyms for Headlong:

adj.

brash (adjective)
madcap, reckless, hotheaded, forward, incautious.
breakneck (adjective)
rapid.
hasty (adjective)
slapdash, urgent, fast.
headlong (adjective)
foolhardy, hurried, impetuous, rash, hasty, brash, impulsive.
rash (adjective)
unconsidered.
reckless (adjective)
rash, reckless, impetuous.

adv.

helter-skelter (adverb)
rashly.
rashly (adverb)
precipitately.

adv

quickly (adverb)
like mad, fast, frenetic, urgent, rapid, like a shot, in a flash/like a flash/quick as a flash, quickly.

n.

down, ascending, bouncy, under, skyward, up, upward, downward. headlong (noun)
headfirst, hurried, forward, hasty, rashly, precipitately.

Other synonyms:

fast, outspread, head first, ill-considered, brash, unconsidered, outstretched, down, temerarious, fetal position. hotheaded, impulsive, incautious, slouch, impetuous, harum-scarum, madcap. improvident, reckless. slapdash. sprawl, stoop. squat. impetuous
foolhardy.
precipitate
rash.

Usage examples for headlong

  1. Yielding to one of my headlong impulses? – The Guilty River by Wilkie Collins
  2. She was young- just twenty- two; she was- she knew it- agreeable to look upon; she had as much money as any reasonable woman need want; she had already seen a great deal of the world outside England; and she had fallen headlong in love with this charming old house, and had now, in spite of various difficulties, managed to possess herself of it, and plant her life in it. – The Testing of Diana Mallory by Mrs. Humphry Ward
  3. Then as she came, still headlong to the river, she heard Harding's voice saying something, she did not know what. – The Flaw in the Crystal by May Sinclair