Beyond a Doubt - thephotogenesis
2. [c] a worry or fear about something
[u] (formal) the fact of being uncertain
Source: Oxford Advanced Learner's Dictionary - 7th Edition
I think that English have so many various choice of words. For example, 'anxiety' can also be described as 'worry' or 'fear'. Another example, 'doubt' have a synonym with 'dubiety', 'hesitation', 'hesitancy', and else. Although it is the same, choosing the right words can be really confusing. It could be that even if it's your mother language, you'll still confused. Well, this is how I feel about my mother language.