'Headfirst' definitions:

Definition of 'headfirst'

From: WordNet
adverb
With the head foremost; "the runner slid headlong into third base" [syn: headlong, headfirst]
adjective
With the head foremost; "a headfirst plunge down the stairs"; "a headlong dive into the pool" [syn: headfirst, headlong]

Definition of 'Headfirst'

From: GCIDE
  • Headfirst \Head`first"\ (h[e^]d"f[~e]rst`), Headforemost \Head`fore"most`\ (h[e^]d`f[=o]r"m[=o]st`), adv. With the head foremost; -- of motion. [1913 Webster]

Synonyms of 'headfirst'

From: Moby Thesaurus