idiot box vs receiving system

idiot box and receiving system both are nouns.

Word	Noun	Adjective	Verb	Adverb
idiot box	Yes	No	No	No
receiving system	Yes	No	No	No

As nouns, receiving system is a hypernym of idiot box; that is, receiving system is a word with a broader meaning than idiot box:

idiot box: an electronic device that receives television signals and displays them on a screen
receiving system: set that receives radio or tv signals

Other hypernyms of idiot box include receiver.

idiot box (noun)	receiving system (noun)
an electronic device that receives television signals and displays them on a screen	set that receives radio or tv signals