A first at university in store - looking back, presumably, that comes with a lot of pain (6)
I believe the answer is:
trauma
'store looking back presumably that comes with a lot of pain' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'a first at university in' is the wordplay.
'first' means one lot of letters go next to another.
'at' becomes 'tram' (I can't justify this - if you can you should believe this answer much more).
'university' becomes 'u'.
'in' means one lot of letters goes inside another.
'tram' placed around 'u' is 'traum'.
'a' put after 'traum' is 'TRAUMA'.
Can you help me to learn more?
(Other definitions for trauma that I've seen before include "Psychological 23" , "Emotional upset" , "Shock to the body or mind" , "Deeply-upsetting shock" , "Physical or mental shock" .)