Cave-dweller (5)
I believe the answer is:
troll
'cave-dweller' is the definition.
(a troll might live in a cave)
This is all the clue.
(Other definitions for troll that I've seen before include "Ugly creature of folklore" , "Mythological being" , "Ugly character from Norse legend" , "Try to catch fish" , "Creature from Norse mythology" .)