early 15c., from Middle French oblique (14c.) and directly from Latin obliquus "slanting, sidelong, indirect," from ob "against" (see ob-) + root of licinus "bent upward," from PIE root *lei- "to bend, be movable" (see limb (n.1)). As a type of muscles, in reference to the axis of the body, 1610s (adj.), 1800 (n.). Related: Obliquely; obliqueness.