Constellation with the star Regulus (3)
I believe the answer is:
leo
'constellation with the star regulus' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for leo that I've seen before include "Lion sign of the Zodiac" , "MGM's lion" , "Pope" , "Astrological sign" , "Cancer, ___, Virgo" .)