"fame, renown, glory," 1799, probably originally in university slang, from Greek kydos "glory, fame," especially in battle, "a poetical word, found chiefly in the Iliad and Odyssey" [Century Dictionary], literally "that which is heard of," perhaps from PIE root *keu- "to see, observe, perceive." In form the word is a Greek singular noun, but the final -s often is mistaken as a plural suffix in English, leading to the barbarous back-formation kudo (attested by 1936).

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."