Sign of summer (3)
I believe the answer is:
leo
'sign of summer' is the definition.
(star sign of July and August)
This is the entire clue.
(Other definitions for leo that I've seen before include "Lion sign of the Zodiac" , "Lion constellation" , "Singer-songwriter Sayer, b. 1949" , "Pope" , "Cancer, ___, Virgo" .)