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1711 (earlier as mastupration, 1620s), from French masturbation and directly from Modern Latin masturbationem (nominative masturbatio), noun of action from past participle stem of Latin masturbari "to masturbate." The long-standing speculation is that this Latin word is altered (probably by influence of turbare "to stir up") from *manstuprare, from manu, ablative of manus "hand" (see manual) + stuprare "defile" (oneself), from stuprum "defilement, dishonor," related to stupere "to be stunned, stupefied" (see stupid). But perhaps the first element represents an unattested *mazdo- "penis" [OED]. An earlier technical word for this was Onanism. Related: Masturbational.
masturbation mas·tur·ba·tion (mās'tər-bā'shən)
Excitation of one's own or another's genital organs, usually to orgasm, by manual contact or means other than sexual intercourse.