Comedy's opening with deity one's seen in Greek play (6)
I believe the answer is:
chorus
'one's seen in greek play' is the definition.
I can't tell whether this defines the answer.
'comedy's opening with deity' is the wordplay.
'comedy's opening' becomes 'c' (I can't justify this - if you can you should believe this answer much more).
'with' means one lot of letters go next to another.
'deity' becomes 'Horus' (Horus is an example).
'c'+'horus'='CHORUS'
Can you help me to learn more?
(Other definitions for chorus that I've seen before include "Group singing together" , "Song's repeated part" , "Some chanting" , "Pipe up in unison" , "Group of voices" .)