sheen (n.)

also *skeu- Proto-Indo-European root meaning "to see, observe, perceive." 

It forms all or part of: Anschauung; caution; cautious; caveat; kudos; precaution; scavenger; scone; sheen; show.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit kavih "wise, sage; seer, poet;" Avestan kauui- "seer, poet, wise man;" Middle Iranian škoh "splendor, majesty;" Latin cautio "care, foresight," cautus "careful, heedful," cavere "beware, take heed;" Greek kydos "glory, fame;" Lithuanian kavoti "tend, safeguard;" Armenian cucanem "I show;" Old Church Slavonic čudo "wonder;" Czech (z)koumati "to perceive, be aware of;" Serbian čuvati "watch, heed;" Old English sceawian "to look at," Middle Dutch schoon "beautiful, bright," properly "showy," Old High German scouwon "to watch."

Middle English sheuen, from Old English sceawian "to look at, see, gaze, behold, observe; inspect, examine; look for, choose," from Proto-Germanic *skauwojanan (source also of Old Saxon skauwon "to look at," Old Frisian skawia, Dutch schouwen, Old High German scouwon "to look at"), from Proto-Germanic root *skau- "behold, look at," from PIE *skou-, variant of root *keu- "to see, observe, perceive."

The causal meaning "let be seen; put in sight, make known" evolved c. 1200 for unknown reasons, seems to be unique to English (German schauen still means "look at"), and in a century displaced the older meaning. The sense of "explain, make clear" is from c. 1300, as the intransitive sense of "be seen, appear."

The spelling shew, popular 18c. and surviving into early 19c., represents an obsolete pronunciation (rhymes with view). The horse-racing sense of "finish third or in the top three" is by 1903, perhaps from an earlier sense in card-playing.