neck and neck vs head-to-head

neck and neck and head-to-head both are adjectives.

Word	Noun	Adjective	Verb	Adverb
neck and neck	No	Yes	No	Yes
head-to-head	No	Yes	No	Yes

As adjectives, neck and neck and head-to-head are synonyms defined as:

neck and neck and head-to-head: inconclusive as to outcome; close or just even in a race or comparison or competition

Other synonyms of neck and neck include nip and tuck.

As adverbs, neck and neck and head-to-head are synonyms defined as:

neck and neck and head-to-head: even or close in a race or competition or comparison

Other synonyms of neck and neck include nip and tuck.

neck and neck (adjective)	head-to-head (adjective)
inconclusive as to outcome; close or just even in a race or comparison or competition	inconclusive as to outcome; close or just even in a race or comparison or competition
	involving two persons; intimately private

neck and neck (adverb)	head-to-head (adverb)
even or close in a race or competition or comparison	even or close in a race or competition or comparison