怀疑 means (1) to doubt, and (2) to suspect. This seems to lead to some confusing translations. For example:
could have two very different translations. If I use "to doubt", then it would translate to
I doubt this 100 yuan bill is fake
Meaning that you think it's real. On the other hand, if I use suspect, it would translate to
I suspect this 100 yuan bill is fake
Meaning you think it's most likely fake. These are nearly complete opposite meanings!
I don't believe my understanding of the word is wrong b/c I've heard it used in both contexts (though I may indeed be wrong), but how am I to know when definition is being applied?