In snake pit a pharaoh's inscribed a message (7)
I believe the answer is:
epitaph
'a message' is the definition.
(epitaph is a kind of message)
'in snake pit a pharaoh's inscribed' is the wordplay.
'in' indicates a hidden word.
'EPITAPH' is hidden in the letters of 'snake pit a pharaohs inscribed'.
(Other definitions for epitaph that I've seen before include "Tomb inscription" , "Words written on tombstone" , "Words written in memory of the dead" , "Words inscribed on a tomb" , "last words" .)