Partner
Middle English: alteration of parcener ‘partner, joint heir’, from Anglo-Norman French parcener, based on Latin partitio(n- ) ‘partition’. The change in the first syllable was due to association with part.
wiktionary
From Middle English partener, partiner, alteration (due to Middle English part) of Middle English parcener, from Old French parçonier, parçonneour(“joint heir”) from parçon(“partition”), from Latin partītiōnem, singular accusative of partītiō(“portion”). The word may also represent Old French part tenour(“part holder”). Compare also Middle English partifere(“partner”), partifelewe(“partner”). Doublet of parcener.
etymonline
partner (n.)
c. 1300, partiner, "a sharer or partaker in anything," altered from parcener (late 13c.), from Old French parçonier "partner, associate; joint owner, joint heir," from parçon "partition, division. portion, share, lot," from Latin partitionem (nominative partitio) "a sharing, partition, division, distribution" from past participle stem of partire "to part, divide" (from pars "a part, piece, a share," from PIE root *pere- (2) "to grant, allot").
The form in English has been influenced by part (n.). The word also may represent Old French part tenour "part holder." From late 14c. as "one who shares power or authority with another;" the commercial sense is by 1520s. Meaning "a husband or wife, one associated in marriage with another" is from 1749.
partner (v.)
1610s, transitive, "to make a partner," from partner (n.). Intransitive sense, "join one another in partnership," is by 1961. Related: Partnered; partnering.
