1610s, "sloping edge," also "groove in which a stone is set," from O.Fr. *besel (13c.; Mod.Fr. biseau), cognate with Sp. bisel; of uncertain origin, perhaps lit. "a stone with two angles," from V.L. *bis-alus, from bis- "twice" + ala "wing, side." Meaning "oblique face of a gem" is from c.1840.