Worm, in turn, met grub (9)
I believe the answer is:
nutriment
'grub' is the definition.
The definition and answer can be both things that one consumes for nourishment as well as being singular nouns.
Maybe there's an association between them I don't understand?
'worm in turn met' is the wordplay.
'in turn met' anagrams to 'NUTRIMENT'.
Though, I'm not sure how this is indicated.
Can you help me to learn more?
(Other definitions for nutriment that I've seen before include "Material providing food" , "diet" , "It sustains" , "Sustenance, nourishment" , "Nourishing food" .)