Leonine lair (3)
I believe the answer is:
den
'leonine lair' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for den that I've seen before include "Animal's lair or man's study" , "Animal lair or gent's study" , "Gentleman's study or animal's lair" , "Lair for animal or study for gent" , "Cave" .)