megalith vs megalithic structure

megalith and megalithic structure both are nouns.

Word	Noun	Adjective	Verb	Adverb
megalith	Yes	No	No	No
megalithic structure	Yes	No	No	No

As nouns, megalith and megalithic structure are synonyms defined as:

megalith and megalithic structure: memorial consisting of a very large stone forming part of a prehistoric structure (especially in western Europe)

megalith (noun)	megalithic structure (noun)
memorial consisting of a very large stone forming part of a prehistoric structure (especially in western Europe)	memorial consisting of a very large stone forming part of a prehistoric structure (especially in western Europe)