Viewer plugged in here (3,6)
I believe the answer is:
eye socket
'viewer plugged in here' is the definition.
I know that 'viewer' relates to this answer. I also know that both the answer and definition are singular nouns
'viewer plugged in here' is the wordplay.
'viewer' becomes 'eye' (organ which sees or views).
'plugged in here' becomes 'socket' (I am not sure about this - if you are sure you should believe this answer much more).
'eye'+'socket'='EYE SOCKET'
(Other definitions for eye socket that I've seen before include "Here viewer's set" , "Cavity for sight organ" , "Hole for viewing organ" , "Orbit (anatomy)" .)