Where does “headfirst” come from?

Headfirst comes from Middle English first and Old English hēafod, from Proto-Germanic furistaz meaning "head," ultimately from Proto-Indo-European kauput-.

headfirst (English): With the head in front; headlong; Rashly;...

Definitions

  1. With the head in front; headlong; Rashly;...

Ancestry of “headfirst”, step by step

headfirst traces back through two separate lines of ancestry.

via English head

StepLanguageWordMeaning
1EnglishheadThe part of the body of an animal or human which...
2English-yAdded to nouns and adjectives to form adjectives...
3Middle English-yDesignates an adjective, in many cases formed by...
4Old English-iġ-y, -ic
5Proto-West Germanic-gForms adjectives from nouns and verbs with a...
6Proto-Germanic-gaz-y
7Proto-Indo-European-ḱos-y, -ic

via English First

StepLanguageWordMeaning
1EnglishFirstPreceding all others of a series or kind; the ordinal of one; earliest
2Middle Englishfirstfirst
3Old EnglishfyrstAlternative form of fierst; Alternative form of...
4Proto-Germanicfrestaz
5Proto-Indo-Europeanpres-to press
6Proto-Indo-Europeanper-before, in front; first; to go through
7Proto-Indo-Europeanpr̥tóspassed , crossed
Every word from Proto-Indo-European -ḱos