tightrope vs high wire

tightrope and high wire both are nouns.

Word	Noun	Adjective	Verb	Adverb
tightrope	Yes	No	No	No
high wire	Yes	No	No	No

As nouns, high wire is a hyponym of tightrope; that is, high wire is a word with a more specific, narrower meaning than tightrope:

tightrope: tightly stretched rope or wire on which acrobats perform high above the ground
high wire: a tightrope very high above the ground

tightrope (noun)	high wire (noun)
tightly stretched rope or wire on which acrobats perform high above the ground	a tightrope very high above the ground