party line vs telephone circuit

party line and telephone circuit both are nouns.

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

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

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

party line (noun)	telephone circuit (noun)
a telephone line serving two or more subscribers	a telephone connection
the policy of a political group