Docker who has dieted? (10)
I believe the answer is:
lighterman
'docker who has dieted?' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
This is the entire clue.
Can you help me to learn more?
(Other definitions for lighterman that I've seen before include "Worker on river" , "Dock worker" .)