Octopus took a month off to write a musical work (4)
I believe the answer is:
opus
'musical work' is the definition.
(synonyms)
'octopus took a month' is the wordplay.
'octopus' becomes 'o' (this could be a standard abbreviation I've not previously seen).
'took' means one lot of letters go next to another.
'a month' becomes 'Pus' (Pus is an example).
'o'+'pus'='OPUS'
'off to write a' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for opus that I've seen before include "Composer's catalogue number" , "Composer's work" , "Work of 25 perhaps" , "Work (mus.)" , "Showing creative skill" .)