protoactinium vs atomic number 91

protoactinium and atomic number 91 both are nouns.

Word	Noun	Adjective	Verb	Adverb
protoactinium	Yes	No	No	No
atomic number 91	Yes	No	No	No

As nouns, protoactinium and atomic number 91 are synonyms defined as:

protoactinium and atomic number 91: a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead

Other synonyms of protoactinium include Pa, protactinium.

protoactinium (noun)	atomic number 91 (noun)
a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead	a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead