Is it ensure, insure, or assure?
early 14c., transitive and intransitive, of uncertain origin, perhaps related to East Frisian rubben "to scratch, rub," and Low German rubbeling "rough, uneven," or similar words in Scandinavian (cf. Danish rubbe "to rub, scrub," Norwegian rubba), of uncertain origin. Related: Rubbed; rubbing.
To rub (someone) the wrong way is from 1853; probably the notion is of cats' fur. To rub noses in greeting as a sign of friendship (attested from 1822) formerly was common among Eskimos, Maoris, and some other Pacific Islanders. Rub out "obliterate" is from 1560s; underworld slang sense of "kill" is recorded from 1848, American English. Rub off "remove by rubbing" is from 1590s; meaning "have an influence" is recorded from 1959.
"act of rubbing," 1610s, from rub (v.); earlier "obstacle, inequality on ground" (1580s, common in 17c.) which is the figure in Hamlet's there's the rub (1602).
The application of friction and pressure.
Such a procedure applied to the body.