cavity vs barbecue pit

cavity and barbecue pit both are nouns.

Word	Noun	Adjective	Verb	Adverb
cavity	Yes	No	No	No
barbecue pit	Yes	No	No	No

As nouns, barbecue pit is a hyponym of cavity; that is, barbecue pit is a word with a more specific, narrower meaning than cavity:

cavity: a sizeable hole (usually in the ground)
barbecue pit: a pit where wood or charcoal is burned to make a bed of hot coals suitable for barbecuing meat

Other hyponyms of cavity include trou-de-loup, borrow pit, divot, fire pit, quicksand, sandpit, sawpit, tar pit.

cavity (noun)	barbecue pit (noun)
(anatomy) a natural hollow or sinus within the body	a pit where wood or charcoal is burned to make a bed of hot coals suitable for barbecuing meat
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