Extra
来自Big Physics
mid 17th century (as an adjective): probably a shortening of extraordinary, suggested by similar forms in French and German.
wiktionary
Abbreviation of extraordinary.
etymonline
extra
1650s as a stand-alone adjective; also used as an adverb and noun in 17c. (see extra-); modern usages -- including sense of "minor performer in a play" (1777) and "special edition of a newspaper" (1793) -- probably all are from shortenings of extraordinary, which in 18c. was used extensively as noun and adverb in places extra would serve today.
