Board not up for school food? (8)
I believe the answer is:
plankton
'school food?' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'board not up' is the wordplay.
'board' becomes 'plank' (synonyms).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'not' back-to-front is 'ton'.
'plank'+'ton'='PLANKTON'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for plankton that I've seen before include "Water micro-organisms" , "drifting masses" , "Drifting ocean organisms" , "Minute fish food" , "Food source for aquatic creatures" .)