Constellation near Hydra (3)
I believe the answer is:
'constellation near hydra' 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 "Singer-songwriter Sayer, b. 1949" , "one of several popes" , "Star sign of one born on August 1" , "of pride" , "Lion sign of the Zodiac" .)