Etymology
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ingenuous (adj.)
1590s, "noble in nature, high-minded; honorably straightforward," from Latin ingenuus "with the virtues of freeborn people, of noble character, frank, upright, candid," originally "native, freeborn," literally "born in (a place)," from in- "in" (from PIE root *en "in") + PIE *gen(e)-wo-, suffixed form of root gene- "to give birth, beget, produce" (see genus). Sense of "artless, innocent" is 1670s, via evolution from "honorably open, straightforward," to "innocently frank." Related: Ingenuously; ingenuousness.
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disingenuous (adj.)

"lacking in candor, insincere; not open, frank, or candid," 1650s, from dis- "opposite of" + ingenuous. Related: Disingenuously; disingenuousness; disenginuity (1640s).

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ingenue (n.)
"young woman who displays innocent candor or simplicity," 1848, from French ingénue "artless girl," especially as a character on the stage, noun use of fem. of ingénu "ingenuous, artless, simple" (13c.), from Latin ingenuus "frank, upright, candid," originally "free-born" (see ingenuous). Italicized in English into 20c.
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ingenuity (n.)

1590s, "honor, nobility," from French ingénuité "quality of freedom by birth" and directly from Latin ingenuitatem (nominative ingenuitas) "condition of a free-born man," figuratively "frankness, generosity, noble-mindedness," from ingenuus "frank, candid, noble" (see ingenuous).

Etymologically, this word belongs to ingenuous, but in 17c. ingenious "intellectual, talented" and ingenuous so often were confused (even by Shakespeare) that ingenuity in English has come to mean only "capacity for invention or construction." That sense of this word is first attested 1640s; the word for it in Middle English was ingeniosity (the native word is craftiness). French ingénuité, meanwhile, has evolved through "natural and graceful freedom of manners" to "graceful simplicity" (compare ingenue); for the sense "ingeniousness," French uses ingéniosité.

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unsophisticated (adj.)
1620s, "unmixed," from un- (1) "not" + sophisticated (adj.). Meaning "ingenuous, natural, inexperienced" is recorded from 1660s.
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artless (adj.)
1580s, "unskillful," from art (n.) + -less. Later also "uncultured, rude" (1590s); then "unartificial, natural" (1670s) and "guileless, ingenuous" (1713). Related: Artlessly; artlessness.
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candid (adj.)
1620s, "white, bright," from Latin candidum "white; pure; sincere, honest, upright," from candere "to shine," from PIE root *kand- "to shine." In English, metaphoric extension to "frank, honest, sincere" first recorded 1670s (compare French candide "open, frank, ingenuous, sincere"). Of photography, "unposed, informal" 1929. Related: Candidly; candidness.
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madrigal (n.)

"short love poem," especially one suitable for music, also "part-song for three or more voices," 1580s, from Italian madrigale, which is of uncertain origin; probably from Venetian dialect madregal "simple, ingenuous," from Late Latin matricalis "invented, original," literally "of or from the womb," from matrix (genitive matricis) "womb" (see matrix).

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naif (adj.)

"ingenuous, artless, natural," 1590s, from French naïf, literally "naive" (see naive). The masculine form of the French word, but used in English without reference to gender. As a noun, "natural, artless, naive person," first attested 1893, from French, where Old French naif also meant "native inhabitant; simpleton, natural fool."

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unmerited (adj.)

1640s, from un- (1) "not" + past participle of merit (v.).

"An ingenuous mind feels in unmerited praise the bitterest reproof. If you reject it you are unhappy, if you accept it you are undone." [Walter Savage Landor, "Imaginary Conversations"]
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