partneryoudaoicibaDictYouDict
partner: [14] Partner is related to part – but not quite so directly as might appear. When it first entered the language it was in the form parcener [13], which remains in existence as a legal term meaning ‘joint heir’. This came via Anglo- Norman parcener ‘partner’ from Vulgar Latin *partiōnārius, a derivative of Latin partītiō ‘partition’ (source of English partition [15]). This in turn was based on the verb partīrī ‘divide up’, a derivative of pars ‘part’. The change from parcener to partner began in the 14th century, prompted by the similarity to part.
=> part, partition
partyyoudaoicibaDictYouDict
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
repart (v.)youdaoicibaDictYouDict
1570s, "divide up," from re- + part (v.). Related: Reparted; reparting.