Distinguish from constellation (4)
I believe the answer is:
tell
'distinguish' is the definition.
(I know that distinguish is a kind of mark)
'from constellation' is the wordplay.
'from' indicates a hidden word.
'TELL' can be found hidden inside 'constellation'.
(Other definitions for tell that I've seen before include "Relate (a story)" , "William ..., skilled Swiss archer" , "Narrate; inform" , "Relate; Swiss hero" , "Count - recount" .)