Be eating the thing making for a light meal (4)
I believe the answer is:
bite
'for a light meal' is the definition.
(I've seen this before)
'be eating the thing' is the wordplay.
'eating' means one lot of letters goes inside another.
'the thing' becomes 'it'.
'be' enclosing 'it' is 'BITE'.
'making' acts as a link.
(Other definitions for bite that I've seen before include "Pungency" , "Clamp down teeth" , "champ" , "Grip with teeth" , "Nip; nibble" .)