Sick Damascene, say, beheaded like some ancient countrymen (8)
I believe the answer is:
illyrian
'like some ancient countrymen' is the definition.
(Illyria was an ancient region)
'sick damascene say beheaded' is the wordplay.
'sick' becomes 'ill' (synonyms).
'damascene say' becomes 'Syrian' (a Damascene is someone from Damascus in Syria).
'beheaded' means to remove the first letter (the head of the word is removed).
'syrian' with its first letter taken away is 'yrian'.
'ill'+'yrian'='ILLYRIAN'
(Other definitions for illyrian that I've seen before include "old foreign language" , "language from Albania" .)