I? I love to eat (6)
I believe the answer is:
iodine
'i?' is the definition.
('iodine' can be a synonym of 'i')
'i love to eat' is the wordplay.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'to eat' becomes 'dine' (dining is a kind of eating).
'i'+'o'+'dine'='IODINE'
(Other definitions for iodine that I've seen before include "Halogen element, atomic no 53" , "Element existing in vapour and crystalline form" , "Element used in medicine, photography and dyes" , "for therapeutic purposes" , "Black/violet element" .)