Eat some food in earnest (4)
I believe the answer is:
dine
'eat' is the definition.
(to dine is to eat a meal)
'some food in earnest' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'DINE' can be found hidden inside 'food in earnest'.
(Other definitions for dine that I've seen before include "Take dinner" , "Eat dinner" , "Eat main meal" , "Have supper" , "Take meal" .)