television set vs idiot box

television set and idiot box both are nouns.

Word	Noun	Adjective	Verb	Adverb
television set	Yes	No	No	No
idiot box	Yes	No	No	No

As nouns, television set and idiot box are synonyms defined as:

television set and idiot box: an electronic device that receives television signals and displays them on a screen

Other synonyms of television set include boob tube, goggle box, television, television receiver, telly, tv, tv set.

television set (noun)	idiot box (noun)
an electronic device that receives television signals and displays them on a screen	an electronic device that receives television signals and displays them on a screen