loop-line vs spur track

loop-line and spur track both are nouns.

Word	Noun	Adjective	Verb	Adverb
loop-line	Yes	No	No	No
spur track	Yes	No	No	No

As nouns, spur track is a hypernym of loop-line; that is, spur track 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
spur track: a railway line connected to a trunk line

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

loop-line (noun)	spur track (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