runic letter vs thorn

runic letter and thorn both are nouns.

Word	Noun	Adjective	Verb	Adverb
runic letter	Yes	No	No	No
thorn	Yes	No	No	No

As nouns, thorn is a hyponym of runic letter; that is, thorn is a word with a more specific, narrower meaning than runic letter:

runic letter: any character from an ancient Germanic alphabet used in Scandinavia from the 3rd century to the Middle Ages
thorn: a Germanic character of runic origin

runic letter (noun)	thorn (noun)
any character from an ancient Germanic alphabet used in Scandinavia from the 3rd century to the Middle Ages	something that causes irritation and annoyance
	a Germanic character of runic origin
	a small sharp-pointed tip resembling a spike on a stem or leaf