Eccentric liable to eat nothing but a flower (7)
I believe the answer is:
lobelia
'a flower' is the definition.
(thesaurus)
'eccentric liable to eat nothing' is the wordplay.
'eccentric' is an anagram indicator.
'to eat' means one lot of letters goes inside another.
'nothing' becomes 'o' (looks like zero - 0).
'liable' anagrammed gives 'lbelia'.
'lbelia' enclosing 'o' is 'LOBELIA'.
'but' is the link.
(Other definitions for lobelia that I've seen before include "Five-lobed flower" , "something flowery" , "Garden plant with five-lobed flowers" , "Flower used for hanging baskets" , "Oil bale (anag) - flower" .)