Garments derived from goats (5)
I believe the answer is:
'garments' is the definition.
(toga is a kind of garment)
'derived from goats' is the wordplay.
'derived from' indicates an anagram.
'goats' is an anagram of 'TOGAS'.
(Other definitions for togas that I've seen before include "What some ancient citizens wore" , "garments worn by ancient Romans" , "Roman garments" , "clothing" .)