Back end (4)
'back end' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tail that I've seen before include "Elongated appendage of an animal" , "Flexible part that extends from an animal's rear" , "Private investigator" , "Follow - dog" , "Rump" .)
'back end' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for rear that I've seen before include "Bring up (children)" , "Bring up - back end" , "Back; bring up (young)" , "Of horse, rise up on hind legs" , "Bottom" .)