1610s, "inclination," from slope, v.. Meaning "an incline, a slant (of ground)" is from 1620s. Derogatory slang meaning "Oriental person" is attested from 1948.

1590s, "go in an oblique direction," from earlier adjective meaning "slanting" (c.1500), probably from Middle English aslope (adv.) "on the incline" (late 15c.), from Old English *aslopen, past participle of aslupan "to slip away," from a- "away" + slupan "to slip" (see sleeve). From 1709 as "to be in a slanting position;" transitive sense "place in a slanting position" is from c.1600. Related: Sloped; sloping.