land line vs telephone line

land line and telephone line both are nouns.

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

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

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

land line (noun)	telephone line (noun)
a telephone line that travels over terrestrial circuits	a telephone connection
	the wire that carries telegraph and telephone signals