Big cat formerly seen around university (5)
I believe the answer is:
ounce
'big cat' is the definition.
(I know that ounce is a type of big cat)
'formerly seen around university' is the wordplay.
'formerly' becomes 'once' (synonyms).
'seen around' is an insertion indicator.
'university' becomes 'U' (abbreviation for university).
'once' going around 'u' is 'OUNCE'.
(Other definitions for ounce that I've seen before include "Approx. twenty-eight gm" , "Small quantity - weight" , "small portion" , "A light imperial measure of weight" , "16 for a pound" .)