portal tomb vs dolmen

portal tomb and dolmen both are nouns.

Word	Noun	Adjective	Verb	Adverb
portal tomb	Yes	No	No	No
dolmen	Yes	No	No	No

As nouns, portal tomb and dolmen are synonyms defined as:

portal tomb and dolmen: a prehistoric megalithic tomb typically having two large upright stones and a capstone

Other synonyms of portal tomb include cromlech.

portal tomb (noun)	dolmen (noun)
a prehistoric megalithic tomb typically having two large upright stones and a capstone	a prehistoric megalithic tomb typically having two large upright stones and a capstone