The study of lions? (3)
I believe the answer is:
den
'the study' is the definition.
(term for a study or office)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for den that I've seen before include "Cave" , "Animals' shelter" , "Home of the beast" , "Room for work or play" , "Animal's lair or gent's study" .)