Merriam-Webster's Collegiate® Dictionary, 11th Edition
STAG
I. noun (plural stags)
Etymology: Middle English stagge, from Old English stagga; akin to Old Norse andarsteggi drake
Date: 12th century
an adult male red deer, a young horse, a male animal castrated after sexual maturity, a young adult male domestic chicken or turkey,
5. a social gathering of men only, one who attends a dance or party without a companion,
II. verb (stagged; stagging)
Etymology: stag (informer)
Date: 1796
transitive verb to spy on, intransitive verb to attend a dance or party without a companion,
III. adjective
Date: 1843
1. restricted to men , intended or suitable for a gathering of men only, unaccompanied by someone of the opposite sex , stag adverb