slater vs pill bug

slater and pill bug both are nouns.

Word	Noun	Adjective	Verb	Adverb
slater	Yes	No	No	No
pill bug	Yes	No	No	No

As nouns, pill bug is a hyponym of slater; that is, pill bug is a word with a more specific, narrower meaning than slater:

slater: any of various small terrestrial isopods having a flat elliptical segmented body; found in damp habitats
pill bug: small terrestrial isopod with a convex segmented body that can roll up into a ball

Other hyponyms of slater include sow bug.

slater (noun)	pill bug (noun)
any of various small terrestrial isopods having a flat elliptical segmented body; found in damp habitats	small terrestrial isopod with a convex segmented body that can roll up into a ball