dolmen vs portal tomb

dolmen and portal tomb both are nouns.

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

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

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

Other synonyms of dolmen include cromlech.

dolmen (noun)	portal tomb (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