Notice vermouth in the passage (4)
I believe the answer is:
adit
'passage' is the definition.
(adit is a kind of passage)
'notice vermouth' is the wordplay.
'notice' becomes 'ad'.
'vermouth' becomes 'it' (short for 'Italian vermouth' as in 'gin and it').
'ad'+'it'='ADIT'
'in the' is the link.
(Other definitions for adit that I've seen before include "Pit access" , "Taking passage" , "Mine-shaft" , "Horizontal mine passage" , "Mine access passage" .)