sandpit vs cavity

sandpit and cavity both are nouns.

Word	Noun	Adjective	Verb	Adverb
sandpit	Yes	No	No	No
cavity	Yes	No	No	No

As nouns, cavity is a hypernym of sandpit; that is, cavity is a word with a broader meaning than sandpit:

Other hypernyms of sandpit include pit.

sandpit (noun)	cavity (noun)
a plaything consisting of a pile of sand or a box filled with sand for children to play in	(anatomy) a natural hollow or sinus within the body
a large pit in sandy ground from which sand is dug	a sizeable hole (usually in the ground)
	soft decayed area in a tooth; progressive decay can lead to the death of a tooth
	space that is surrounded by something