Tries or fails to make merry (7)
I believe the answer is:
roister
'make merry' is the definition.
(roistering is a kind of making merry)
'tries or fails' is the wordplay.
'fails' indicates anagramming the letters (a failed spelling).
'tries'+'or'='triesor'
'triesor' is an anagram of 'ROISTER'.
'to' is the link.
(Other definitions for roister that I've seen before include "Behave boisterously" , "Enfold" , "I rest or (anag) - engage in noisy merrymaking" , "Noisy reveller" , "Rioters (anag.)" .)