Suffuse each chicken, say, with root of liquorice (8)
I believe the answer is:
permeate
'suffuse' is the definition.
(I've seen this in another clue)
'each chicken say with root of liquorice' is the wordplay.
'each' becomes 'per' ('per' can mean for each).
'chicken say' becomes 'meat' (chicken is a kind of meat).
'with' says to put letters next to each other.
'root of' suggests the final letters (in a down clue, the letter at the bottom).
The final letter of 'liquorice' is 'e'.
'per'+'meat'+'e'='PERMEATE'
(Other definitions for permeate that I've seen before include "Spread throughout" , "Spread or pervade" , "Flow or spread into every part of" , "Seep through" , "Soak through" .)