capital punishment vs death penalty

capital punishment and death penalty both are nouns.

Word	Noun	Adjective	Verb	Adverb
capital punishment	Yes	No	No	No
death penalty	Yes	No	No	No

As nouns, capital punishment and death penalty are synonyms defined as:

capital punishment and death penalty: putting a condemned person to death

Other synonyms of capital punishment include executing, execution.

capital punishment (noun)	death penalty (noun)
putting a condemned person to death	putting a condemned person to death