a male deer.
Merriam-Webster Online Dictionary
stag (noun)1.
an adult male red deer , also the male of various other deer (especially genus ) - Cervus
2.
chiefly Scottish a young horse , especially a young unbroken stallion
3.
a male animal castrated after sexual maturity - compare steer 1
4.
a young adult male domestic chicken or turkey
5.
a) a social gathering of men only
b) one who attends a dance or party without a companion
transitive verb
intransitive verb
British to spy on to attend a dance or party without a companion
1.
a) restricted to men - a stag party
b) intended for a male audience , especially - pornographic stag movies
2.
unaccompanied by someone of the opposite sex - stag women