Regarded as part of a play, say (4)
I believe the answer is:
seen
'regarded' is the definition.
(I've seen this in another clue)
'part of a play say' is the wordplay.
'part of a play' becomes 'scene' ('scene' is part of 'play').
'say' shows a homophone (sound like).
'scene' is a homophone of 'SEEN'.
'as' is the link.
(Other definitions for seen that I've seen before include "Met - understood" , "Viewed" , "Noticed" , "Observed or percieved" , "Distinguished" .)