Key to cut out for conduit (4)
I believe the answer is:
duct
'for conduit' is the definition.
(duct is a kind of conduit)
'key to cut out' is the wordplay.
'key' becomes 'd' (musical key).
'to' says to put letters next to each other.
'out' indicates an anagram (out can mean wrong or inaccurate).
'cut' is an anagram of 'uct'.
'd'+'uct'='DUCT'
(Other definitions for duct that I've seen before include "Tube for cables, air, etc" , "Enclosed conduit for fluid" , "Tube for conveing cable, liquid etc" , "Pipe, tube" , "Air passage" .)