Supply teacher for the most part a goddess (6)
I believe the answer is:
hecate
'a goddess' is the definition.
(I've seen this before)
'supply teacher for the most part' is the wordplay.
'supply' indicates an anagram (in a supple way).
'for the most part' means to remove the last letter (most but not all of the letters).
'teacher' with its last letter taken away is 'teache'.
'teache' is an anagram of 'HECATE'.
(Other definitions for hecate that I've seen before include "Goddess of dark places gets the ace" , "Divine witch" , "evil witch" , "Greek goddess of witchcraft and ghosts" , "Greek goddess associated with witchcraft and the ghost world" .)