Stag

1. An adult male deer.
2. A colt, or filly.
3. (by extension) A romping girl; a tomboy.
4. An improperly or late castrated bull or ram – also called a bull seg (see note under ox).
5. An outside irregular dealer in stocks, who is not a member of the exchange.
6. One who applies for the allotment of shares in new projects, with a view to sell immediately at a premium, and not to hold the stock.
7. The Eurasian wren, Troglodytes troglodytes.
8. (usually attributive) An unmarried male, a bachelor; a male not accompanying a female at a social event.

   a stag dance; a stag party

9. A social event for males held in honor of a groom on the eve of his wedding, attended by male friends of the groom, sometimes a fund-raiser.

   The stag will be held in the hotel's ballroom.

10. A stag beetle (family Lucanidae).
11. Guard duty.

1. To act as a "stag", an irregular dealer in stocks.
2. To watch; to dog, or keep track of.

adverb

Of a man, attending a formal social function without a date.