noun, na-adjective
Refers to a lack of honesty or integrity in character or behavior. Can be used as a noun or adjectival noun.
彼の不正直な態度にはがっかりした。
I was disappointed by his dishonest attitude.
不正直は信頼を失う原因になる。
Dishonesty causes a loss of trust.
嘘つき is a more colloquial term for a liar, focusing on telling lies, while 不正直 is a broader term for dishonesty in character.
Formed from 不 (negative prefix) + 正直 (honesty). The derivation is straightforward; the word has been used in Japanese for centuries.