A deep-seated tendency to suspect others' motives; often used in psychological or literary contexts. 猜疑心が強い is a common collocation.
He is very suspicious and doesn't trust people easily.
Out of suspicion, I couldn't take my friend's words at face value.
猜疑心 refers to a deep-seated, persistent distrust of others, while 疑心 is a more general term for a feeling of doubt or suspicion.
猜疑 (suspicion) + 心 (heart/mind). 猜疑 is a compound of 猜 (envy, jealousy) and 疑 (doubt).