Suspicion is a feeling that something might be true. If your friends seem to be keeping a secret from you, you might have a suspicion that they are planning a surprise party for your birthday.
Suspicion can mean the same as hunch or inkling, like when you have a suspicion that your friend is hiding a flower bouquet behind his back. Suspicion comes from the Latin word suspicere, or mistrust. That's why it can mean a general bad feeling about someone or something, like neighbors who regard all new people with suspicion until they get to know them.