Gaunt eccentric eating nothing sweet (6)
I believe the answer is:
nougat
'sweet' is the definition.
(nougat is a kind of sweet)
'gaunt eccentric eating nothing' is the wordplay.
'eccentric' is an anagram indicator.
'eating' is an insertion indicator.
'nothing' becomes 'o' (looks like zero - 0).
'gaunt' anagrammed gives 'nugat'.
'nugat' placed around 'o' is 'NOUGAT'.
(Other definitions for nougat that I've seen before include "Honey/nuts sweet" , "Type of sweet" , "Chewy pink or white sweet" , "Type of confection" , "Hard, chewy sweet" .)