Curtail break and work to go over puzzle (5)
I believe the answer is:
poser
'puzzle' is the definition.
(I've seen this before)
'curtail break and work to go over' is the wordplay.
'curtail' means to remove the last letter (I've seen 'curtailed' mean this).
'break' becomes 'rest' (resting is a kind of breaking).
'and' is a charade indicator (letters next to each other).
'work' becomes 'op' (abbreviation for opus).
'to go over' says the letters should be written in reverse.
'rest' with its last letter removed is 'res'.
'res'+'op'='resop'
'resop' in reverse letter order is 'POSER'.
(Other definitions for poser that I've seen before include "Baffling question or problem" , "Attitudiniser" , "Problem to be solved" , "question master?" , "Pseud" .)