tumulus vs grave mound

tumulus and grave mound both are nouns.

Word	Noun	Adjective	Verb	Adverb
tumulus	Yes	No	No	No
grave mound	Yes	No	No	No

As nouns, tumulus and grave mound are synonyms defined as:

tumulus and grave mound: (archeology) a heap of earth placed over prehistoric tombs

Other synonyms of tumulus include barrow, burial mound.

tumulus (noun)	grave mound (noun)
(archeology) a heap of earth placed over prehistoric tombs	(archeology) a heap of earth placed over prehistoric tombs