Word Origin & History
1520s, from Fr. biais "slant, oblique," also figuratively, "expedient, means" (13c., in O.Fr. "sideways, askance, against the grain"), from O.Prov. biais, with cognates in Old Catalan and Sardinian; possibly from V.L. *(e)bigassius, from Gk. epikarsios "athwart, crosswise, at an angle," from epi- "upon"
+ karsios "oblique," from PIE *krs-yo-, from base *(s)ker- "to cut." A pp. adjective that became a noun in Old French. Transferred sense of "predisposition, prejudice" is from 1570s.
"[A] technical term in the game of bowls, whence come all the later uses of the word." [OED]
The verb is from 1620s.