Communication in a muddle a long time (7)
I believe the answer is:
message
'communication' is the definition.
(message is a kind of communication)
'a muddle a long time' is the wordplay.
'a muddle' becomes 'mess' (synonyms).
'a long time' becomes 'age' ('age' can be a synonym of 'long time').
'mess'+'age'='MESSAGE'
'in' acts as a link.
(Other definitions for message that I've seen before include "Brief communication" , "meaning" , "Missive" , "Errand" , "Spoken or written communication" .)