candid vs heart-to-heart

candid is not a noun while heart-to-heart is a noun.

Word	Noun	Adjective	Verb	Adverb
candid	No	Yes	No	No
heart-to-heart	Yes	Yes	No	No

As adjectives, candid and heart-to-heart are synonyms defined as:

candid and heart-to-heart: openly straightforward and direct without reserve or secretiveness

Other synonyms of candid include open.

candid (noun)	heart-to-heart (noun)
	an intimate talk in private

candid (adjective)	heart-to-heart (adjective)
characterized by directness in manner or speech; without subtlety or evasion	openly straightforward and direct without reserve or secretiveness
openly straightforward and direct without reserve or secretiveness
informal or natural; especially caught off guard or unprepared