headfirst vs headlong

headfirst and headlong both are adjectives.

Word	Noun	Adjective	Verb	Adverb
headfirst	No	Yes	No	Yes
headlong	No	Yes	No	Yes

As adjectives, headfirst and headlong are synonyms defined as:

As adverbs, headfirst and headlong are synonyms defined as:

headfirst (adjective)	headlong (adjective)
with the head foremost	with the head foremost
	excessively quick

headfirst (adverb)	headlong (adverb)
with the head before the body	with the head before the body
	in a hasty and foolhardy manner
	at breakneck speed