Constant yen for a drop of Cointreau in pub (5)
I believe the answer is:
loyal
'constant' is the definition.
(thesaurus)
'yen for a drop of cointreau in pub' is the wordplay.
I cannot quite see how this works, but
'yen' could be 'y' and 'y' is found within the answer.
'a' is found in the answer.
'of' could be 'o' and 'o' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for loyal that I've seen before include "Steadfast and true" , "Sort of toast" , "Keeping faith" , "Showing enduring firm support" , "Faithful (in allegiance)" .)