1650s, "having white and brown (or some other color) patches, spotted in an irregular manner" (used especially of horses), from skued "skewbald" (mid-15c.), of unknown origin, + bald "having white patches" (see bald). First element said to be unconnected with skew (v.) (but Klein's sources say it is); OED suggests perhaps from Old French escu "shield," but also notes a close resemblance in form and sense with Icelandic skjottr, "the history of which is equally obscure." Watkins says it is Scandinavian and akin to Old Norse sky "cloud" on the resemblance of the markings to cloud cover.
When the white is mixed with black it is called 'pie-bald,' with bay the name of 'skew-bald' is given to it. ["Youatt's 'The Horse,' " 1866]
As a noun meaning "skewbald horse" from 1863.