"a part or portion," Middle English del, from from Old English dæl "a part of a whole, a share;" with qualification (great, etc.), "an extent, degree, quantity, amount," from Proto-Germanic *dailaz (source also of Old Norse deild, Old Frisian del "part; juridical district," Dutch deel, Old High German and German teil, Gothic dails "part, share, portion"), from PIE *dail- "to divide" (source also of Old Church Slavonic delu, Lithuanian dalis "part"), ‌‌perhaps a Northern Indo-European extended form of the root *da- "to divide," or perhaps a substratum word.

Formerly used in many senses now taken by part. Meaning "a share (of something), one's allotted portion" is from c. 1200. Business sense of "transaction, bargain" is 1837, originally slang, from the older sense of "arrangement among a number of persons for mutual advantage." In American history, New Deal is from Franklin D. Roosevelt's speech of July 2, 1932 (the phrase itself is by 1834). Big deal is from 1928 as "important transaction;" ironic use first recorded 1951 in "Catcher in the Rye." Deal-breaker is attested by 1975.

late 14c., champertie, champartie, the illegal act whereby a person not otherwise interested makes a bargain to maintain a litigant in return for a share of the property in dispute if the case succeeds. It is a transferred use, from Old French champart "portion of produce received by a feudal lord from land held in lease from him" (13c.), from Medieval Latin campipartem, from campi pars "part of the field" (see campus + part (n.)).

also fore-part, c. 1400, from fore- + part (n.).

late 14c. as "indivisible, incapable of being parted," from Medieval Latin impartibilis; see im- "not, opposite of" + part (v.). From 1630s as "capable of being imparted," from impart (v.) + -ible. Now little used in either sense.

1550s, in grammar, "to state the part of speech of a word or the words in a sentence," a verbal use of Middle English pars (n.) "part of speech" (c. 1300), from Old French pars, plural of part "a part," from Latin pars "a part, piece" (from PIE root *pere- (2) "to grant, allot") in the school question, Quae pars orationis? "What part of speech?" Transferred (non-grammatical) use is by 1788. Pars also was a common plural of part (n.) in early Middle English. Related: Parsed; parsing.

"one who takes or has a part or share in common with others," c. 1400, part-taker, "a sharer, a participant," from part (n.) + agent noun from take (v.); see partake.

mid-13c., "the act of going away, departure;" c. 1300, "separation of persons, leave-taking," also "the act of dividing or putting asunder; distribution, apportionment;" verbal noun from part (v.). From late 14c. as "the act or process of dividing; a division or separation; a dividing line, a point or place of separation or division."

"in part, in some measure or degree, not wholly," 1520s, from part (n.) + -ly (2).

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.

"personal qualities, gifts of ability, share of mental endowments or acquirements," 1560s, from part (n.).