trunk line vs telephone line

trunk line and telephone line both are nouns.

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

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

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

trunk line (noun)	telephone line (noun)
a telephone line connecting two exchanges directly	a telephone connection
line that is the main route on a railway	the wire that carries telegraph and telephone signals