Keep going in university after second bad mark (7)
I believe the answer is:
sustain
'keep going' is the definition.
(thesaurus)
'university after second bad mark' is the wordplay.
'university' becomes 'u'.
'after' is a charade indicator (letters next to each other).
'second' becomes 's' (common abbreviation).
'bad' indicates anagramming the letters.
'mark' becomes 'stain' ('stain' can be a synonym of 'mark'**).
'u'+'s'='us'
'us' with letters rearranged gives 'su'.
'su'+'stain'='SUSTAIN'
'in' acts as a link.
(Other definitions for sustain that I've seen before include "Nurture, uphold" , "Keep up; hold for a long time" , "Support, keep going" , "Strengthen physically" , "Strengthen, support" .)