Most of a piece of cake eaten by poor farm workers (8)
I believe the answer is:
peasants
'farm workers' is the definition.
'most of a piece of cake eaten by poor' is the wordplay.
'most of' means to remove the last letter.
'a piece of cake' becomes 'easy' (I've seen this before).
'eaten by' means one lot of letters goes inside another.
'poor' becomes 'pants'.
'easy' with its last letter taken off is 'eas'.
'eas' placed within 'pants' is 'PEASANTS'.
(Other definitions for peasants that I've seen before include "Old tillers of the soil" , "People farming small-scale" , "Old rustic workers" , "uncultured people" , "bumpkins" .)