na-adjective, noun
honest; frank; straightforward
Describes a person, statement, or attitude that is truthful and without deception. Often used as a compliment or self-description.
彼はとても正直な人だ。
He is a very honest person.
正直に言うと
To be honest, I don't really like it.
adverb
Adverbial use, often at the beginning of a sentence to express one's true feelings or admit something.
正直、もう疲れたよ。
Honestly, I'm tired already.