Jelly snake, I see (5)
I believe the answer is:
aspic
'jelly' is the definition.
(aspic is a kind of jelly)
'snake i see' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'see' becomes 'c' (the word for the letter, according to Chambers).
'asp'+'i'+'c'='ASPIC'
(Other definitions for aspic that I've seen before include "Clear meat or fish jelly" , "Setter" , "that's clear?" , "Savoury jelly for coating meats and eggs" , "Stock set with food" .)