WATS vs telephone circuit

WATS and telephone circuit both are nouns.

Word	Noun	Adjective	Verb	Adverb
WATS	Yes	No	No	No
telephone circuit	Yes	No	No	No

As nouns, telephone circuit is a hypernym of WATS; that is, telephone circuit is a word with a broader meaning than WATS:

WATS: a telephone line; long distance service at fixed rates for fixed zones; an acronym for wide area telephone service
telephone circuit: a telephone connection

Other hypernyms of WATS include line, phone line, subscriber line, telephone line.

WATS (noun)	telephone circuit (noun)
a telephone line; long distance service at fixed rates for fixed zones; an acronym for wide area telephone service	a telephone connection