i-adjective
suspicious; distrustful; incredulous
Describes a person who habitually doubts others' words or motives; often used for a skeptical or wary nature.
彼は疑い深い性格で、人の言うことをすぐには信じない。
He has a suspicious nature and doesn't easily believe what people say.
そんなに疑い深くならなくてもいいじゃないか。
You don't have to be so distrustful.