shirttail vs appendix

shirttail and appendix both are nouns.

Word	Noun	Adjective	Verb	Adverb
shirttail	Yes	No	No	No
appendix	Yes	No	No	No

As nouns, appendix is a hypernym of shirttail; that is, appendix is a word with a broader meaning than shirttail:

shirttail: a brief addendum at the end of a newspaper article
appendix: supplementary material that is collected and appended at the back of a book

shirttail (noun)	appendix (noun)
fabric forming the tail of a shirt	a vestigial process that extends from the lower end of the cecum and that resembles a small pouch
a brief addendum at the end of a newspaper article	supplementary material that is collected and appended at the back of a book