Gogglebox (5)
'gogglebox' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for television that I've seen before include "Gogglebox" , "box set" , "Tube" .)
(Other definitions for telly that I've seen before include "'The box' (colloquial)" , "One of the media" , "The goggle-box" , "Television" , "- - Savalas" .)