DSL vs telephone circuit

DSL and telephone circuit both are nouns.

Word	Noun	Adjective	Verb	Adverb
DSL	Yes	No	No	No
telephone circuit	Yes	No	No	No

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

DSL: a generic name for digital lines that are provided by telephone companies to their local subscribers and that carry data at high speeds
telephone circuit: a telephone connection

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

DSL (noun)	telephone circuit (noun)
a generic name for digital lines that are provided by telephone companies to their local subscribers and that carry data at high speeds	a telephone connection