Mountain pass in Monaco, likely enough (3)
I believe the answer is:
col
'mountain pass' is the definition.
(col is a kind of mountain pass)
'in monaco likely enough' is the wordplay.
'in' indicates a hidden word.
'COL' can be found hidden inside 'monaco likely enough'.
(Other definitions for col that I've seen before include "Feature of mountain" , "Mountain saddle" , "Officer" , "Pass between hills" , "Lowest point of ridge between two peaks" .)