Exploit us before early start (3)
I believe the answer is:
use
'exploit' is the definition.
(use can mean to exploit)
'us before early start' is the wordplay.
'before' means one lot of letters go next to another.
'start' suggests taking the first letters.
The initial letter of 'early' is 'e'.
'us'+'e'='USE'
(Other definitions for use that I've seen before include "Benefit" , "Manipulate" , "Application" , "Milk" , "Consumption" .)