varnish vs coating

varnish and coating both are nouns.

Word	Noun	Adjective	Verb	Adverb
varnish	Yes	No	Yes	No
coating	Yes	No	No	No

As nouns, coating is a hypernym of varnish; that is, coating is a word with a broader meaning than varnish:

varnish: a coating that provides a hard, lustrous, transparent finish to a surface
coating: a thin layer covering something

Other hypernyms of varnish include coat.

varnish (noun)	coating (noun)
a coating that provides a hard, lustrous, transparent finish to a surface	the work of applying something
	a thin layer covering something
	a heavy fabric suitable for coats
	a decorative texture or appearance of a surface (or the substance that gives it that appearance)

varnish (verb)	coating (verb)
cover with varnish