death penalty vs capital punishment

death penalty and capital punishment both are nouns.

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

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

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

Other synonyms of death penalty include executing, execution.

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