tablet vs slab

tablet and slab both are nouns.

Word	Noun	Adjective	Verb	Adverb
tablet	Yes	No	No	No
slab	Yes	No	No	No

As nouns, slab is a hypernym of tablet; that is, slab is a word with a broader meaning than tablet:

tablet (noun)	slab (noun)
a dose of medicine in the form of a small pellet	block consisting of a thick piece of something
a small flat compressed cake of some substance
a slab of stone or wood suitable for bearing an inscription
a portable computer with a touchscreen
a number of sheets of paper fastened together along one edge