Dog may pass to rest (6)
I believe the answer is:
collie
'dog' is the definition.
(collie is a kind of dog)
'pass to rest' is the wordplay.
'pass' becomes 'col' (col is a kind of pass).
'to rest' becomes 'lie' (lying is a kind of resting).
'col'+'lie'='COLLIE'
'may' is the link.
(Other definitions for collie that I've seen before include "Breed of sheepdog" , "Popular kind of sheepdog" , "Scottish sheep dog" , "Type of sheepdog" , "shepherd's gofer" .)