Doubt search is initially working (8)
I believe the answer is:
question
'doubt' is the definition.
(I know that doubt can be written as question)
'search is initially working' is the wordplay.
'search' becomes 'quest' (quest is a kind of search).
'initially' suggests taking the first letters.
'working' becomes 'on' (on can mean working or activated).
The initial letter of 'is' is 'i'.
'quest'+'i'+'on'='QUESTION'
(Other definitions for question that I've seen before include "motion for debate" , "Doubt; object to" , "Interrogate or express doubt about" , "Pump" , "Call into doubt" .)