par·ty 
(pärtē)
(pärtē)n. pl. par·ties
1. A social gathering especially for pleasure or amusement: a birthday party.
2.
a. A group of people who have gathered to participate in an activity: a search party.
b. A group of soldiers selected for a duty or mission: a raiding party.
3. An established political group organized to promote and support its principles and candidates for public office.
4.
a. A person or group involved in an enterprise; a participant or accessory: I refuse to be a party to your silly scheme.
b. Law A person or entity that participates in a transaction, makes a contract, or is involved in a lawsuit as a litigant.
5.
a. A subscriber to a telephone party line.
b. A person using a telephone.
6. A person: "And though Grainger was a spry old party, such steps couldn't be his" (Anthony Hyde).
adj.
1. Of, relating to, or participating in an established political organization: party members; party politics.
2. Suitable for use at a social gathering: party dresses; a party hat.
3. Characteristic of a pleasurable social gathering: a party atmosphere.
intr.v. par·tied, par·ty·ing, par·ties
To celebrate or carouse at a party or similar gathering: That night we partied until dawn.
[Middle English partie, part, side, group, from Old French, from feminine past participle of partir, to divide, from Latin partīre, from pars, part-, part; see PART.]
parti·er, party·er n.