Definitions:

1. at breakneck speed adverb
   • burst headlong through the gate
2. in a hasty and foolhardy manner adverb
   • I fell headlong in love with my neighbor.
3. with the head foremost adverb
   • the runner slid headlong into third base

Synonyms:

• hasty
• headfirst
• headlong
• hell-for-leather
• rashly