loop-line vs branch line

loop-line and branch line both are nouns.

Word	Noun	Adjective	Verb	Adverb
loop-line	Yes	No	No	No
branch line	Yes	No	No	No

As nouns, branch line is a hypernym of loop-line; that is, branch line is a word with a broader meaning than loop-line:

loop-line: a railway branch line that branches from the trunk line and then rejoins it later on
branch line: a railway line connected to a trunk line

Other hypernyms of loop-line include spur, spur track.

loop-line (noun)	branch line (noun)
a railway branch line that branches from the trunk line and then rejoins it later on	a railway line connected to a trunk line