Liquid food thus finished (4)
I believe the answer is:
soup
'liquid food' is the definition.
(I've seen this before)
'thus finished' is the wordplay.
'thus' becomes 'so' (synonyms).
'finished' becomes 'up' (eg 'time's up' means the time is finished).
'so'+'up'='SOUP'
(Other definitions for soup that I've seen before include "Preliminary course" , "See 19" , "First course" , "liquid content in this food" , "Mulligatawny or borscht?" .)