Called work great at first (4)
I believe the answer is:
rung
'called' is the definition.
(I've seen this before)
'work great at first' is the wordplay.
'work' becomes 'run' (both can mean to operate something).
'at first' suggests taking the first letters.
The initial letter of 'great' is 'g'.
'run'+'g'='RUNG'
(Other definitions for rung that I've seen before include "Part of a ladder" , "Tolled - step on ladder" , "Ladder's step" , "Telephoned" , "Horizontal bar in ladder" .)