Fellow worker (9)
'fellow worker' is the definition.
(synonyms)
This is all the clue.
(Other definitions for colleague that I've seen before include "fellow member of staff" , "Partner's" , "Workmate" , "China, perhaps" , "Associate" .)
'fellow worker' is the definition.
(I've seen this before)
'fellow worker' is the wordplay.
I cannot really understand how this works, but
'fellow' could be 'co' (eg a co-worker is a fellow worker) and 'co' is found within the answer.
'worker' could be 'rat' (rat is a kind of worker) and 'rat' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for collaborator that I've seen before include "Fellow worker" , "who takes part in jobshare?" , "Partner" , "Fellow-worker" , "Quisling" .)