early 15c., "rejected as worthless," from Late Latin reprobatus, past participle of reprobare "disapprove, reject, condemn," from Latin re- "back, again," here perhaps indicating "opposite of, reversal of previous condition" (see re-) + probare "prove to be worthy" (see probate (n.)). The meaning "abandoned in character, morally depraved, unprincipled" is by 1650s.
as an intensive execration, "odious, detestable, damned," 1650s, past-participle adjective from confound in its older sense of "condemn, curse," which came to be considered "a milder form of imprecation" [OED]. It is perhaps a euphemism for damned. The sense of "put to mental confusion" is recorded from mid-14c.
Middle English dampnen, also damnen, dammen, late 13c. as a legal term, "to condemn, declare guilty, convict;" c. 1300 in the theological sense of "doom to punishment in a future state," from Old French damner "damn, condemn; convict, blame; injure," derivative of Latin damnare "to adjudge guilty; to doom; to condemn, blame, reject," from noun damnum "damage, hurt, harm; loss, injury; a fine, penalty," from Proto-Italic *dapno-, possibly from an ancient religious term from PIE *dap- "to apportion in exchange" [Watkins] or *dhp-no- "expense, investment" [de Vaan]. The -p- in the English word disappeared 16c.
The legal meaning "pronounce judgment upon" evolved in the Latin word. The optative expletive use likely is as old as the theological sense. Damn and its derivatives generally were avoided in print from 18c. to 1930s (the famous line in the film version of "Gone with the Wind" was a breakthrough and required much effort by the studio). Meaning "judge or pronounce (a work) to be bad by public expression" is from 1650s; to damn with faint praise is from Pope.
The noun is recorded from 1610s, "utterance of the word 'damn.'" To be not worth a damn is from 1817. To not give (or care) a damn is by 1760. The adjective is 1775, short for damned; Damn Yankee, the characteristic Southern U.S. term for "Northerner," is attested by 1812 (as damned). Related: Damning.
c. 1300, dampnacioun, "condemnation to Hell by God," also "fact of being condemned by judicial sentence," from Old French damnation, from Latin damnationem (nominative damnatio), noun of action from past-participle stem of damnare "to doom, condemn" (see damn). As an imprecation, attested from c. 1600.
Damnation follows death in other men,
But your damn'd Poet lives and writes agen.
[Pope, letter to Henry Cromwell, 1707 or 1708]
c. 1400, reprobacioun, "rejection," from Church Latin reprobationem (nominative reprobatio) "rejection, reprobation," noun of action from past-participle stem of reprobare "disapprove, reject, condemn" (see reprobate (adj.)).
In theology, "the state of being consigned to eternal punishment" (1530s). From 1580s as "condemnation as worthless or spurious;" the broad sense of "condemnation, censure, act of vehemently disapproving" is from 1727. Other nouns that have been used in English include reprobacy (1590s), reprobance (c. 1600), reprobature (1680s, legal).
Men condemn corsets in the abstract, and are sometimes brave enough to insist that the women of their households shall be emancipated from them; and yet their eyes have been so generally educated to the approval of the small waist, and the hourglass figure, that they often hinder women who seek a hygienic style of dress. [Mary Ashton Rice Livermore, "The Story of My Life," 1898]
mid-14c., reproche, "a rebuke, blame, censure" directed against a person; also "object of scorn or contempt;" c. 1400, as "disgrace, state of disgrace," from Anglo-French repruce, Old French reproche "blame, shame, disgrace" (12c.), from reprochier "to blame, bring up against."
OED cites Diez for the explanation that this is from Vulgar Latin *repropiare, from Latin re- "opposite of" + prope "near" (see propinquity), with suggestions of "bring near to" as in modern get in (someone's) face. But it points out other etymologists of French would have it from *reprobicare, from Latin reprobus/reprobare "disapprove, reject, condemn" (see reprobate (adj.)).