Very large device (4)
I believe the answer is:
tool
'device' is the definition.
(I've seen this before)
'very large' is the wordplay.
'very' becomes 'too' (I've seen this before).
'large' becomes 'l'.
'too'+'l'='TOOL'
(Other definitions for tool that I've seen before include "Hand implement" , "Cat's-paw; impress design on" , "Appliance" , "one of 12 [SPADES] , for example" , "Working instrument" .)