Rabbit's home (6)
'rabbit's home' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for burrow that I've seen before include "A rabbit's tunnel" , "Hole or tunnel built by a rabbit, say" , "Hole dug by a small animal" , "Hole in the ground made by an animal" , "Animal's hole or tunnel" .)
(Other definitions for warren that I've seen before include "boy" , "densely populated area" , "Network of caves as built by rabbits" , "Maze of passages" , "Connecting burrows" .)