One goes in break to take exam again (5)
I believe the answer is:
resit
'take exam again' is the definition.
(sit an exam again)
'one goes in break' is the wordplay.
'one' becomes 'i' (Roman numeral).
'goes in' indicates putting letters inside.
'break' becomes 'rest' (a rest is taking a break).
'i' going into 'rest' is 'RESIT'.
'to' acts as a link.
(Other definitions for resit that I've seen before include "repeated test" , "Exam taken again" , "take another exam" , "later exam" , "second exam" .)