Pronunciation: (hed'lông", -long"),[key] —adv. 1. with the head foremost; headfirst: to plunge headlong into the water. 2. without delay; hastily: to plunge headlong into work. 3. without deliberation; rashly: to rush headlong into battle.
—adj. 1. undertaken quickly and suddenly; made precipitately; hasty: a headlong flight. 2. rash; impetuous: a headlong denunciation. 3. done or going with the head foremost: a headlong dive into the pool.