partyyoudaoicibaDictYouDict[party 词源字典]
party: [13] The Latin verb partīrī ‘divide up’ was derived from pars ‘part’ (source of English part). The feminine form of its past participle, partīta, was used in Vulgar Latin as a noun meaning ‘part, side’, and passed into English via Old French partie. This was later reinforced by Old French parti, which came from the Vulgar Latin neuter form *partītum and contributed the English word’s more salient current senses ‘political group’ and (in the 18th century) ‘social gathering’.

Other contributions made to English by the Latin past participle are the element -partite of words like bipartite, tripartite, etc and (via Italian) the musical term partita [19].
=> part[party etymology, party origin, 英语词源]
party (n.)youdaoicibaDictYouDict
late 13c., "part, portion, side," from Old French partie "side, part; portion, share; separation, division" (12c.), literally "that which is divided," noun use of fem. past participle of partir "to divide" (see part (v.)). Political sense of "side in a contest or dispute" evolved by 1300; meaning "a person" is from mid-15c. Sense of "gathering for social pleasure" is first found 1716, from general sense of persons gathered together (originally for some specific purpose, such as dinner party, hunting party). Phrase the party is over is from 1937; party line is first recorded 1834 in the sense of "policy adopted by a political party," 1893 in the sense of "telephone line shared by two or more subscribers." Party pooper is from 1951, American English.
party (v.)youdaoicibaDictYouDict
"have a good time," 1922, from party (n.). Earlier as "to take the side of" (1630s). Related: Partied; partying.