trunk line vs subscriber line

trunk line and subscriber line both are nouns.

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

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

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

trunk line (noun)	subscriber line (noun)
a telephone line connecting two exchanges directly	a telephone connection
line that is the main route on a railway