monument vs empty tomb

monument and empty tomb both are nouns.

Word	Noun	Adjective	Verb	Adverb
monument	Yes	No	No	No
empty tomb	Yes	No	No	No

As nouns, empty tomb is a hyponym of monument; that is, empty tomb is a word with a more specific, narrower meaning than monument:

monument: a structure erected to commemorate persons or events
empty tomb: a monument built to honor people whose remains are interred elsewhere or whose remains cannot be recovered

monument (noun)	empty tomb (noun)
a structure erected to commemorate persons or events	a monument built to honor people whose remains are interred elsewhere or whose remains cannot be recovered
a burial vault (usually for some famous person)
an important site that is marked and preserved as public property