Definition of "headfirst"

headfirst

adverb
not comparable
1. With the head in front; headlong.
2. Rashly; precipitately; without deliberation; hastily.
  Quotations
  Sheffield was not going to stop being Sheffield just because he had dived headfirst into the lusts of the flesh.
  2016, Kerry Greenwood, Murder and Mendelssohn, Sydney: Allen and Unwin, page 245
adjective
not comparable
1. With the head in front; headlong.