early 14c., "outer garment," from Old French cote "coat, robe, tunic, overgarment," from Frankish *kotta "coarse cloth" or some other Germanic source (compare Old Saxon kot "woolen mantle," Old High German chozza "cloak of coarse wool," German Kotze "a coarse coat"), of unknown origin. Transferred to animal's natural covering late 14c. Extended 1660s to a layer of any substance covering any surface. Spanish, Portuguese cota, Italian cotta are Germanic loan-words.

late 14c., "to provide with a coat," from coat, n.. Meaning "to cover with a substance" is from 1753. Related: Coated; coating.