Capsule of cyanide on food portion (5)
I believe the answer is:
piece
'portion' is the definition.
(piece is a kind of portion)
'capsule of cyanide on food' is the wordplay.
'capsule of' says to hollow out the word (remove centre letters) (the letters which encase the word are used).
'on' is a charade indicator (letters next to each other).
'food' becomes 'pie' (pie is a kind of food**).
'cyanide' with its middle taken out is 'ce'.
'ce' put after 'pie' is 'PIECE'.
(Other definitions for piece that I've seen before include "newspaper article" , "Slice" , "Chessman - part - firearm" , "Portion, bit" , "Part - portion" .)