College certainly not over for some workers (5)
I believe the answer is:
union
'some workers' is the definition.
(a unionised workforce)
'college certainly not over' is the wordplay.
'college' becomes 'uni' (I've seen this in other clues).
'certainly not' becomes 'no'.
'over' shows that the letters should be reversed in order.
'no' written backwards gives 'on'.
'uni'+'on'='UNION'
'for' is the link.
(Other definitions for union that I've seen before include "Marriage or alliance" , "Combination" , "Conjunction" , "Jack may join when on the staff" , "Agreement -- wedlock" .)