It nourishes teachers ultimately content with nothing in Paris (8)
I believe the answer is:
nutrient
'it nourishes' is the definition.
'teachers ultimately content with nothing in paris' is the wordplay.
'teachers' becomes 'nut' (National Union of Teachers).
'ultimately' says to take the final letters.
'with' is a charade indicator (letters next to each other).
'nothing in paris' becomes 'rien' ('nothing' in French).
The last letter of 'content' is 't'.
't' after 'rien' is 'rient'.
'nut'+'rient'='NUTRIENT'
(Other definitions for nutrient that I've seen before include "Something providing nourishment" , "Good food" , "vitamin maybe" , "Substance to give energy and build tissue" , "Feeding" .)