Difficult being merry (5)
I believe the answer is:
tight
This clue is a double definition.
'difficult' is the first definition.
(similar in meaning)
'being merry' is the second definition.
(both can mean drunk)
(Other definitions for tight that I've seen before include "Difficult and problematic" , "Close-fitting; tense" , "Awkward" , "Strictly imposed; drunk" , "Constricted - intoxicated" .)