"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.

"plank or board," especially of fir or pine, late 14c., dele, from Low German (compare Middle Low German dele), from Proto-Germanic *theljon." From late 13c. in surnames. An Old English derivative was þelu "hewn wood, board, flooring."

Middle English delen, from Old English dælan "to divide, distribute, separate;" hence "to share with others, bestow, dispense," and also "take part in, have to do with," from Proto-Germanic *dailjanan (source also of Old Saxon deljan, Old Frisian dela "to divide, distribute," Middle Dutch, Dutch deelen, German teilen, Gothic dailjan), from PIE *dail- "to divide," ‌‌perhaps a Northern Indo-European extended form of root *da- "to divide," or a word from a substrate language.

Meaning "to deliver (to another) as his share" is from c. 1300. Meaning "to distribute cards before a game" is from 1520s (the associated noun meaning "distribution of cards before a game" is from c. 1600). Hence colloquial deal (someone) in "include in an undertaking" (1942).

To deal with "handle, act toward (in some way)" is attested from mid-15c., from the notion of "engage in mutual intercourse, have to do with;" in late 14c. the phrase also mean "have sexual intercourse with." Related: Dealt; dealing.

1860s, "a good deal, a large amount;" by 1878 in financial speculation, originally in California publications; see deal (n.1). As an ironic expression, popular in American English from c. 1965, perhaps a translated Yiddishism (such as a groyser kunst).

also mis-deal, 1746, "to make an incorrect distribution in dealing (cards);" from mis- (1) "badly, wrongly" + deal (v.). The noun, "a wrong deal in cards, a deal in which the players do not all receive the proper number of cards in the proper order," is attested from 1793. The original verbal sense (late 15c.) was "to distribute unfairly." Related: Misdealt; misdealing.

*dā-, Proto-Indo-European root meaning "to divide."

It might form all or part of: betide; daimon; Damocles; deal (v.); deal (n.1) "part, portion;" demagogue; demiurge; democracy; demography; demon; demotic; dole; endemic; epidemic; eudaemonic; geodesic; geodesy; ordeal; pandemic; pandemonium; tidal; tide (n.) "rise and fall of the sea;" tidings; tidy; time; zeitgeist.

It might also be the source of: Sanskrit dati "cuts, divides;" Greek dēmos "people, land," perhaps literally "division of society," daiesthai "to divide;" Old Irish dam "troop, company;" Old English tid "point or portion of time," German Zeit "time."

Old English dælere "divider, distributor; agent, negotiator," agent noun from deal (v.). Meaning "player who passes out the cards in a game" is from c. 1600; meaning "one whose business is to buy and sell merchandise" is from 1610s. Meaning "purveyor of illegal drugs" is recorded by 1920.

"to some degree (usually smaller or lesser), some degree or amount of, somewhat," Middle English som-del, obsolete in Modern English or reverting to two words, but very common in Old English as sume dæle "some portion; somewhat," probably adverbial use of a noun phrase, from some + deal (n.1).

past tense and past participle of deal (v.).

c. 1300, trēten (intrans.), "negotiate, debate or discuss for the purpose of settling a dispute;" late 14c. as "bargain, deal with;" from Old French traitier "deal with, act toward; set forth" in speech or writing (12c.). This is from Latin tractare "manage, handle, deal with, conduct oneself (in a certain manner) toward," literally "drag about, tug, haul, pull violently," frequentative of trahere (past participle tractus) "to pull, draw" (see tract (n.1)). Compare entreat.

The sense of "deal with, handle, or develop in speech or writing" is from early 14c.; in reference to tangible objects, "deal with or touch physically," late 14c. The use in medicine "attempt to heal or cure, to manage in the application of remedies," is by early 15c. (Chauliac); one of the Middle English senses of treat (n.) was "medicinal salve" (late 14c.).

The meaning "entertain with food and drink without expense to the recipient by way of compliment, good will or kindness" is by 1710. Related: Treated; treating.