guinea pig vs doer

guinea pig and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
guinea pig	Yes	No	No	No
doer	Yes	No	No	No

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

guinea pig: a person who is subjected to experimental or other observational procedures; someone who is an object of investigation
doer: a person who acts and gets things done

Other hypernyms of guinea pig include actor, worker.

guinea pig (noun)	doer (noun)
stout-bodied nearly tailless domesticated cavy; often kept as a pet and widely used in research	a person who acts and gets things done
a person who is subjected to experimental or other observational procedures; someone who is an object of investigation