'dom' is 'dumb', the opposite of 'slim'(smart)' 'Stom' is a little bit stronger like 'stupid'.
Stom can also be used to express that something is disliked when used by little children: 'Ik vind school stom' ('I think school is stupid'). Grown-ups will typically use more colourful expressions.
It can also means 'silent' in some contexts like 'een stomme film' (a silent movie). 'Hij is doofstom' ('He's deaf-mute')
"Daft" in (British) English is the same as "stupid", but it isn't accepted. I have reported it. (If it is wrong, how would "daft" be translated into Dutch?
I wrote "That is not a dumb question" and it was marked wrong. It seems dumb and stupid are pretty equivalent and we have not learned the Dutch word for dumb. It is natural to call a question dumb in class, it is nicer than stupid. I think it should be included in correct answers until a difference is taught.