One doesn't dream about stars? (7)
I believe the answer is:
realist
'one doesn't dream' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'about stars?' is the wordplay.
'about' becomes 're' (regarding).
'stars?' becomes 'alist' (I can't justify this - if you can you should give a lot more credence to this answer).
're'+'alist'='REALIST'
Can you help me to learn more?
(Other definitions for realist that I've seen before include "One's practically inclined" , "Practical type" , "Sensible and practical person" , "One has no fancy ideas" , "Retails like practical person" .)