party

1250–1300; Middle English partie < Old French, noun use of feminine of parti, past participle of partir < Latin partīre to share. See part

1. See company.

Party meaning “a specific individual” is old in the language, going back to the 15th century, and was formerly in common use. Today, it remains standard in limited senses, chiefly the legal, and is often used humorously or condescendingly: the party holding the balloon. The word person is the neutral and common term.

English party, with its many senses, comes from Old French partie, whose many meanings include “part, side, portion,” literally, “something that has been divided or separated.” In form, partie is the noun use of the feminine past participle of partir “to leave, go, take off, start” (and many other senses). Partir comes from Latin partīre (also partīrī ), whose relatively few meanings include “to share, distribute, divide, divide up.”
Since the 1300s, party has taken on a number of useful meanings, including “any of the people engaged in a formal legal proceeding,” which dates from the early 14th century. First noted in the 17th century is the sense of “an organized political group or faction” ( the Party, short for "the Communist Party," would show up around 1919). Also dating from the 17th century is the term party wall, “a wall that forms a boundary between areas with different owners,” while the familiar “festive social gathering” sense of party can be traced back to the early 18th century. In the next century, party line emerged (during the 1830s) as a political term meaning “a policy or principle to be maintained,” and later (from the early 1890s) was more commonly used in the now obsolete sense of “a telephone line shared by several subscribers.”