early 15c., from M.Fr. oblique, from L. obliquus "slanting, sidelong, indirect," from ob "against" + root of licinus "bent upward," from PIE base *lei- "to bend, be movable" (see limb
(1)). As a type of muscles, in reference to the axis of the body, 1610s (adj.), 1800 (n.). Related: Obliquely.