partner (n.) Look up partner at Dictionary.com
c.1300, 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" (see partition (n.)). Form in English influenced by part (n.). The word also may represent Old French part tenour "part holder."
partner (v.) Look up partner at Dictionary.com
1610s, transitive, "to make a partner," from partner (n.). Intransitive sense from 1961. Related: Partnered; partnering.