skate vs roller skate

skate and roller skate both are nouns.

Word	Noun	Adjective	Verb	Adverb
skate	Yes	No	Yes	No
roller skate	Yes	No	Yes	No

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

skate: sports equipment that is worn on the feet to enable the wearer to glide along and to be propelled by the alternate actions of the legs
roller skate: a shoe with pairs of rollers fixed to the sole

Other hyponyms of skate include ice skate, in-line skate.

As verbs, roller skate is a hyponym of skate; that is, roller skate is a word with a more specific, narrower meaning than skate:

skate: move along on skates
roller skate: travel on shoes with steel or rubber rollers attached to their soles

Other hyponyms of skate include ice skate, figure skate, skateboard, Rollerblade.

skate (noun)	roller skate (noun)
large edible rays having a long snout and thick tail with pectoral fins continuous with the head; swim by undulating the edges of the pectoral fins	a shoe with pairs of rollers fixed to the sole
sports equipment that is worn on the feet to enable the wearer to glide along and to be propelled by the alternate actions of the legs

skate (verb)	roller skate (verb)
move along on skates	travel on shoes with steel or rubber rollers attached to their soles