Spice Girl supporting teachers’ union (6)
I believe the answer is:
nutmeg
'spice' is the definition.
(nutmeg is a kind of spice)
'girl supporting teachers' union' is the wordplay.
'girl' becomes 'Meg'.
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'teachers' union' becomes 'nut' (National Union of Teachers. I am not sure about the 'teachers'' bit.).
'meg' after 'nut' is 'NUTMEG'.
Can you help me to learn more?
(Other definitions for nutmeg that I've seen before include "Hard fruit and girl for a spice" , "One grated as spice" , "Fragrant seed of tropical tree grated as spice" , "Spice for grating" , "Aromatic seasoning" .)