Distinguish from a constellation (4)
I believe the answer is:
tell
'distinguish' is the definition.
('tell' can be a synonym of 'distinguish')
'from a constellation' is the wordplay.
'from' indicates the answer is hidden within the clue.
'TELL' can be found hidden inside 'constellation'.
(Other definitions for tell that I've seen before include "toxophilite" , "his hitting the apple?" , "Make a difference" , "Issue instructions" , "blow the whistle" .)