atomic number 91 vs protoactinium

atomic number 91 and protoactinium both are nouns.

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

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

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

Other synonyms of atomic number 91 include Pa, protactinium.

atomic number 91 (noun)	protoactinium (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