registrant vs doer

registrant and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
registrant	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of registrant; that is, doer is a word with a broader meaning than registrant:

registrant: a person who is formally entered (along with others) in a register (and who obtains certain rights thereby)
doer: a person who acts and gets things done

Other hypernyms of registrant include actor, worker.

registrant (noun)	doer (noun)
a person who is formally entered (along with others) in a register (and who obtains certain rights thereby)	a person who acts and gets things done