early 14c., porcioun, "allotted part, part assigned or attributed, share," also "lot, fate, destiny," from Old French porcion "part, portion" (12c., Modern French portion) and directly from Latin portionem (nominative portio) "share, part," accusative of the noun in the phrase pro portione "according to the relation (of parts to each other)," ablative of *partio "division," related to pars "a part, piece, a share, a division" (from PIE root *pere- (2) "to grant, allot").
Meaning "a part of a whole" is from mid-14c. From late 14c. in the general sense of "section into which something is divided."
"to divide in portions," mid-14c., porciounen, from Old French porcioner "share out, divide in portions," from porcion "part, portion" (see portion (n.)), and directly from Medieval Latin portionare. Related: Portioned; portioning.
*perə-, Proto-Indo-European root meaning "to grant, allot" (and reciprocally, "to get in return"); possibly related to *pere- (1) "to produce, procure."
It forms all or part of: apart; apartment; bipartient; bipartisan; bipartite; compartment; depart; department; ex parte; impart; jeopardy; multipartite; parcel; parse; part; partial; participate; participation; particle; particular; particulate; partisan; partition; partitive; partner; party; portion; proportion; quadripartite; repartee; tripartite.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit purtam "reward;" Hittite parshiya- "fraction, part;" Greek peprotai "it has been granted;" Latin partem (nominative pars) "a part, piece," portio "share, portion."
c. 1200, pitaunce, "pious donation to a religious house or order to provide extra food; the extra food provided," also "a small portion, scanty rations," from Old French pitance "pity, mercy, compassion; refreshment, nourishment; portion of food allowed a monk or poor person by a pious bequest," apparently literally "pity," from the source pity. Perhaps via Medieval Latin *pietantia, from an assumed verb *pietare, or otherwise derived from Latin pietas. Meaning "small amount, portion, or quantity" is attested by 1560s.
mid-15c. (from late 13c. in Anglo-French), "property which a woman brings to her husband at marriage," from Old French doaire "dower, dowry, gift" (see dowry). In modern legal use, "portion of a late husband's real property allowed to a widow for her life." Meaning "one's portion of natural gifts" is from late 14c.