secret ballot vs ballot

secret ballot and ballot both are nouns.

Word	Noun	Adjective	Verb	Adverb
secret ballot	Yes	No	No	No
ballot	Yes	No	Yes	No

As nouns, ballot is a hypernym of secret ballot; that is, ballot is a word with a broader meaning than secret ballot:

secret ballot: a vote in which each person's choice is secret but the totaled votes are public
ballot: a choice that is made by counting the number of people in favor of each alternative

Other hypernyms of secret ballot include balloting, vote, voting.

secret ballot (noun)	ballot (noun)
a vote in which each person's choice is secret but the totaled votes are public	a choice that is made by counting the number of people in favor of each alternative
	a document listing the alternatives that is used in voting

secret ballot (verb)	ballot (verb)
	vote by ballot