The difference between Bachelor party and Stag

Bachelor party as a noun (US, Canada, South Africa):

A party held for a man who is about to be married.

Stag as a noun:

An adult male deer.

Stag as a noun:

A colt, or filly.

Stag as a noun (by extension, obsolete):

A romping girl.

Stag as a noun:

An improperly or late castrated bull or ram – also called a bull seg (see note under ox).

Stag as a noun:

An outside irregular dealer in stocks, who is not a member of the exchange.

Stag as a noun:

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.

Stag as a noun:

The Eurasian wren, Troglodytes troglodytes.

Stag as a noun (usually, _, attributive):

An unmarried male, a bachelor; a male not accompanying a female at a social event.

Stag as a noun:

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.

Stag as a noun:

A stag beetle (family ).

Stag as a verb (intransitive, British):

To act as a "stag", an irregular dealer in stocks.

Stag as a verb (transitive):

To watch; to dog, or keep track of.

Stag as an adverb:

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