television set vs telly

television set and telly both are nouns.

Word	Noun	Adjective	Verb	Adverb
television set	Yes	No	No	No
telly	Yes	No	No	No

As nouns, television set and telly are synonyms defined as:

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

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

television set (noun)	telly (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