semicentenary vs semicentennial

semicentenary and semicentennial both are nouns.

Word	Noun	Adjective	Verb	Adverb
semicentenary	Yes	Yes	No	No
semicentennial	Yes	Yes	No	No

As adjectives, semicentenary and semicentennial are synonyms defined as:

semicentenary and semicentennial: of or relating to or marking the 50th anniversary

As nouns, semicentenary and semicentennial are synonyms defined as:

semicentenary and semicentennial: the 50th anniversary (or the celebration of it)

semicentenary (noun)	semicentennial (noun)
the 50th anniversary (or the celebration of it)	the 50th anniversary (or the celebration of it)

semicentenary (adjective)	semicentennial (adjective)
of or relating to or marking the 50th anniversary	of or relating to or marking the 50th anniversary