Succubus

google

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late Middle English: from medieval Latin succubus ‘prostitute’, from succubare, from sub- ‘under’ + cubare ‘to lie’.

wiktionary

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Alteration in Middle English (based on incubusm) of Late Latin succubaf(“ strumpet, especially a mythological fiend in female form who has intercourse with men in their sleep”), from Latin succubare(“to lie under”), from sub-(“under”) + cubare(“to lie down”), from Proto-Indo-European *keu(b)(“to bend, to turn”).

etymonline

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succubus (n.)

late 14c., alteration (after incubus, giving a masc. form to a word generally felt as of female meaning) of Late Latin succuba "strumpet," applied to a fiend (generally in female form) having sexual connection with men in their sleep, from succubare "to lie under," from assimilated form of sub "under" (see sub-) + cubare "to lie down" (see cubicle). Related: Succubine (adj.).