fiction vs untruth

fiction and untruth both are nouns.

Word	Noun	Adjective	Verb	Adverb
fiction	Yes	No	No	No
untruth	Yes	No	No	No

As nouns, untruth is a hypernym of fiction; that is, untruth is a word with a broader meaning than fiction:

Other hypernyms of fiction include falsehood, falsity.

fiction (noun)	untruth (noun)
a literary work based on the imagination and not necessarily on fact	a false statement
a deliberately false or improbable account