Is it farther or further?
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.