reading vs skim

reading and skim both are nouns.

Word	Noun	Adjective	Verb	Adverb
reading	Yes	No	No	No
skim	Yes	Yes	Yes	No

As nouns, skim is a hyponym of reading; that is, skim is a word with a more specific, narrower meaning than reading:

reading: the cognitive process of understanding a written linguistic message
skim: reading or glancing through quickly

Other hyponyms of reading include speed-reading, perusal, perusing, poring over, studying, browse, browsing, skimming.

reading (noun)	skim (noun)
the act of measuring with meters or similar instruments	reading or glancing through quickly
the cognitive process of understanding a written linguistic message	a thin layer covering the surface of a liquid
a mental representation of the meaning or significance of something
a datum about some physical state that is presented to a user by a meter or similar instrument
written material intended to be read
a particular interpretation or performance
a public instance of reciting or repeating (from memory) something prepared in advance

reading (adjective)	skim (adjective)
	used of milk and milk products from which the cream has been removed

reading (verb)	skim (verb)
	read superficially
	move or pass swiftly and lightly over the surface of
	remove from the surface
	cause to skip over a surface
	coat (a liquid) with a layer
	travel on the surface of water
	examine hastily