Terribly ill specialist into soup seed (6)
I believe the answer is:
lentil
'soup seed' is the definition.
(I've seen this in another clue)
'terribly ill specialist into' is the wordplay.
'terribly' indicates an anagram.
'specialist' becomes 'ent' (Ear, Nose and Throat specialist).
'into' indicates putting letters inside.
'ill' is an anagram of 'lil'.
'lil' placed around 'ent' is 'LENTIL'.
(Other definitions for lentil that I've seen before include "Edible leguminous plant seed" , "Round flat seed" , "Food stuff" , "'Seed, pulse (6)'" , "Type of soup" .)