land line vs telephone circuit

land line and telephone circuit both are nouns.

Word	Noun	Adjective	Verb	Adverb
land line	Yes	No	No	No
telephone circuit	Yes	No	No	No

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

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

land line (noun)	telephone circuit (noun)
a telephone line that travels over terrestrial circuits	a telephone connection