1 to guess

1 a suspect

1 to doubt (sth)

2 to be skeptical of

3 to have one's doubts

4 to harbor suspicions

5 to suspect that

1 unsuspecting

2 innocent and without apprehension

1 no doubt

2 undoubtedly

1 to believe firmly without any doubt (idiom)

2 absolute certainty about sth

1 cannot be doubted (idiom)

1 cannot be doubted (idiom)