late 12c., probably from Old English stagga "a stag," from Proto-Germanic *stag-, from PIE *stegh- "to prick, sting" (see sting (v.)). The Old Norse equivalent was used of male foxes, tomcats, and dragons; and the Germanic root word perhaps originally meant "male animal in its prime." Meaning "pertaining to or composed of males only" (stag party) is American English slang from 1848. Stag film "pornographic movie" is attested from 1968. Stag beetle, so called for its" horns," is from 1680s.
