noun
Refers to a person who tells lies, often used in a mild or childish context. Can be used as a light accusation or teasing term.
あの子は嘘つきだから、信用できない。
That kid is a liar, so I can't trust them.
嘘つきは泥棒の始まり。
Lying is the first step to stealing (proverb).
noun
lying; telling lies
Refers to the act of lying itself, often used in phrases like 嘘つきは… or in contexts discussing the behavior rather than labeling a person.
嘘つきはよくないことだと教える。
We teach that lying is a bad thing.