Salt egg with ceremony (7)
I believe the answer is:
nitrite
'salt' is the definition.
(nitrite is a kind of salt)
'egg with ceremony' is the wordplay.
'egg' becomes 'nit' (nit is a kind of egg).
'with' says to put letters next to each other.
'ceremony' becomes 'rite' (rite is a kind of ceremony).
'nit'+'rite'='NITRITE'
(Other definitions for nitrite that I've seen before include "Radical" , "compound" , "salt" , "Chemical" .)