protactinium vs protoactinium

protactinium and protoactinium both are nouns.

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

As nouns, protactinium and protoactinium are synonyms defined as:

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

Other synonyms of protactinium include atomic number 91, Pa.

protactinium (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