While a student, hard to enter firm (8)
I believe the answer is:
although
'while' is the definition.
(thesaurus)
'a student hard to enter firm' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'hard' becomes 'h'.
'to enter' means one lot of letters goes inside another.
'firm' becomes 'tough' (**).
'h' inserted inside 'tough' is 'though'.
'a'+'l'+'though'='ALTHOUGH'
(Other definitions for although that I've seen before include "Despite the fact that (8)" , "Whilst" , "Notwithstanding" , "Yet" , "Apart from the fact that" .)