oblique (adj.)

early 15c., "slanting, sloping, sideways; crooked, not straight or direct," originally of muscles or eyes, from Old French oblique (14c.) and directly from Latin obliquus "slanting, sidelong, indirect," which is perhaps from ob "against" (see ob-) + root of licinus "bent upward," from a PIE root meaning"to bend, be movable," the source of see limb (n.1). But De Vaan writes, "The etymology is unknown. Closest in form and meaning are līmus 'transverse' and sublīmis 'transverse from below upward', and the latter would be morphologically similar to oblīquus. Yet a root *lī- with different suffixes *-mo- and *-kwo- does not immediately make sense, and has no clear connections outside Italic." 

 Figurative sense of "indirect" is from early 15c. As a noun in anatomy in reference to a type of muscle the direction of whose fibers is oblique to the long axis of the body or to the long axis of the part acted, by 1838. Related: Obliquely; obliqueness.

Definitions of oblique
oblique (n.)
any grammatical case other than the nominative;
Synonyms: oblique case
oblique (n.)
a diagonally arranged abdominal muscle on either side of the torso;
Synonyms: external oblique muscle / musculus obliquus externus abdominis / abdominal external oblique muscle
oblique (adj.)
slanting or inclined in direction or course or position--neither parallel nor perpendicular nor right-angled;
the oblique rays of the winter sun
the axis of an oblique cone is not perpendicular to its base
acute and obtuse angles are oblique angles
oblique (adj.)
indirect in departing from the accepted or proper way; misleading;
gave oblique answers to direct questions
oblique political maneuvers
Synonyms: devious