protoactinium vs protactinium

protoactinium and protactinium both are nouns.

Word	Noun	Adjective	Verb	Adverb
protoactinium	Yes	No	No	No
protactinium	Yes	No	No	No

As nouns, protoactinium and protactinium are synonyms defined as:

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

Other synonyms of protoactinium include atomic number 91, Pa.

protoactinium (noun)	protactinium (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