Wanting to eat grass? Empty Guernsey would eat it (6)
I believe the answer is:
greedy
'wanting to eat' is the definition.
(greed can mean wanting too much food)
'grass? empty guernsey would eat it' is the wordplay.
'grass?' becomes 'reed' (I've seen this before).
'empty' means to remove the middle letters.
'would eat it' indicates putting letters inside.
'guernsey' with its centre taken out is 'gy'.
'reed' going within 'gy' is 'GREEDY'.
(Other definitions for greedy that I've seen before include "Overeating" , "Very eager to get" , "Covetous, avaricious" , "Wanting too much" , "Having excessive desire for food or money" .)