Tom, first in exam -- magic speller? (6)
I believe the answer is:
hecate
'magic speller?' is the definition.
The definition suggests a singular noun which matches the answer.
'tom first in exam' is the wordplay.
I cannot really understand how this works, but
'tom' could be 'cat' (I have seen 'A tom ' mean 'cat' so perhaps 'tom' could also mean 'cat') and 'cat' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hecate that I've seen before include "underworld figure" , "Female with spells" , "Greek goddess of witchcraft and ghosts" , "Greek goddess of the Underworld" , "Greek goddess associated with witchcraft and the ghost world" .)