Important place to handle cargo, we hear (3)
I believe the answer is:
key
'important' is the definition.
(I know that important can be written as key)
'place to handle cargo we hear' is the wordplay.
'place to handle cargo' becomes 'quay' (platform for unloading ships).
'we hear' shows a homophone (sound like).
'quay' sounds like 'KEY'.
(Other definitions for key that I've seen before include "Piano lever" , "Coral reef off southern coast of Florida" , "Device for lock" , "Lock-opener" , "Crucially important" .)