early 15c., "small service book used by a priest," from Old French manuel "handbook" (also "plow-handle"), from Late Latin manuale "case or cover of a book, handbook," noun use of neuter of Latin manualis "of or belonging to the hand; that can be thrown by hand," from manus "hand, strength, power over; armed force; handwriting," from PIE root *man- (2) "hand." Meaning "a concise handbook" of any sort is from 1530s. The etymological sense is "small book such as may be carried in the hand or conveniently used by one hand."
"of or pertaining to the hand; done, made, or used by hand;" c. 1400, from Latin manualis "of or belonging to the hand; that can be thrown by hand," from manus "hand, strength, power over; armed force; handwriting," from PIE root *man- (2) "hand." The military manual exercise (1760) is "the art of handling the rifle and other arms with precision and according to the prescribed method."
"deliberate erotic self-stimulation," 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 disturb, confuse") 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). Hence the earliest form of the word in English. But perhaps the first element represents an unattested *mazdo- "penis" [OED]. An earlier technical word for this was onanism. Related: Masturbational.
Farmer and Henley ["Slang and Its Analogues," 1898] lists among the slang terms for "to masturbate" or "masturbation" frig (which they trace to Latin fricare "to rub") to bob; to box the Jesuit; to chuff, to chuffer; to claw; to digitate (of women); to fight one's turkey (Texan); to handle; to indorse; to milk; to mount a corporal and four; to dash one's doodle; and they note that it was "sometimes known as KEEPING DOWN THE CENSUS."