Sign of fierce animal returning in jumbo, elephant (3)
I believe the answer is:
leo
'sign of fierce animal' is the definition.
(I know that Leo is a astrological sign)
'returning in jumbo elephant' is the wordplay.
'returning' says the letters should be written in reverse.
'in' indicates the answer is hidden within the clue.
'oel' is hidden in the letters of 'jumbo elephant'.
'oel' backwards is 'LEO'.
(Other definitions for leo that I've seen before include "born in July or August" , "Horoscope sign" , "Cancer, ___, Virgo" , "Man" , "Lion sign of the Zodiac" .)