Merrymaking composer pens the ultimate in music, rejecting secure articles (12)
I believe the answer is:
bacchanalian
'merrymaking' is the definition.
'in music rejecting secure articles' is the wordplay.
'in music' becomes 'bacch' (I can't explain this - if you can you should give a lot more credence to this answer).
'rejecting' says the letters should be written in reverse (I've seen 'reject' mean this).
'secure' becomes 'nail' (I've seen this before).
'articles' becomes 'ana' (a and an are indefinite articles).
'nail'+'ana'='nailana'
'nailana' back-to-front is 'analian'.
'bacch'+'analian'='BACCHANALIAN'
'composer pens the ultimate' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
(Other definitions for bacchanalian that I've seen before include "description of drunken revels" , "Relating to drunken revelry" , "drunken reveller" , "Drunken, orgiastic (revel)" .)