for questions which a dictionary cannot answer asking the meaning of a particular expression.
This is the definition of the tag expressions on this site, and as far as I am aware, which a dictionary cannot answer and asking the meaning of a particular expression are both modifiers to questions.
But, could the introduction also be changed to one of the following alternatives?
for questions which a dictionary cannot answer that ask the meaning of a particular expression
for questions asking the meaning of a particular expression which a dictionary cannot answer
for questions that ask the meaning of a particular expression which a dictionary cannot answer
And finally, my second question is, does any of the alternatives sound unnatural?