Very short time to keep in university, being dim (5)
I believe the answer is:
vague
'being dim' is the definition.
(thesaurus)
'very short time to keep in university' is the wordplay.
'short' suggests taking the first letters.
'time' becomes 'age' (age is a kind of time**).
'to keep in' is an insertion indicator.
'university' becomes 'u'.
The first letter of 'very' is 'v'.
'age' placed around 'u' is 'ague'.
'v'+'ague'='VAGUE'
(Other definitions for vague that I've seen before include "Amorphous" , "Indeterminate" , "Rough" , "Unclearly defined" , "Nebulous" .)