WATS vs telephone line

WATS and telephone line both are nouns.

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

As nouns, telephone line is a hypernym of WATS; that is, telephone line 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 line: a telephone connection

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

WATS (noun)	telephone line (noun)
a telephone line; long distance service at fixed rates for fixed zones; an acronym for wide area telephone service	a telephone connection
	the wire that carries telegraph and telephone signals