Spell isn't broken on time (5)
I believe the answer is:
stint
'spell' is the definition.
(thesaurus)
'isn't broken on time' is the wordplay.
'broken' indicates an anagram.
'on' is an insertion indicator (as in clothing \'on\' a person).
'time' becomes 't'.
'isnt' is an anagram of 'sint'.
'sint' placed around 't' is 'STINT'.
(Other definitions for stint that I've seen before include "Prescribed share of work" , "Be sparing; sandpiper" , "Assignment" , "Fixed amount - allowance" , "Limitation of effort" .)