Millions partake of flesh (4)
I believe the answer is:
meat
'flesh' is the definition.
(I have seen 'Edible flesh' mean 'meat' so perhaps 'flesh' could also mean 'meat')
'millions partake of' is the wordplay.
'millions' becomes 'm' (abbreviation).
'partake of' becomes 'eat' (I've seen this before).
'm'+'eat'='MEAT'
(Other definitions for meat that I've seen before include "Chops, steaks etc" , "Spam, ham, lamb etc" , "Flesh for eating" , "The flesh of animals as food" , "Animal flesh as food" .)