Extremely large implement (4)
I believe the answer is:
tool
'implement' is the definition.
(I've seen this before)
'extremely large' is the wordplay.
'extremely' becomes 'too' (I've seen this in other clues).
'large' becomes 'l'.
'too'+'l'='TOOL'
(Other definitions for tool that I've seen before include "Person exploited" , "Device used for work" , "For example, saw" , "Instrument, implement" , "Gun" .)