excuse vs short letter

excuse and short letter both are nouns.

Word	Noun	Adjective	Verb	Adverb
excuse	Yes	No	Yes	No
short letter	Yes	No	No	No

As nouns, short letter is a hypernym of excuse; that is, short letter is a word with a broader meaning than excuse:

Other hypernyms of excuse include billet, line, note.

excuse (noun)	short letter (noun)
a poor example	a short personal letter
a defense of some offensive behavior or some failure to keep a promise etc.
a note explaining an absence

excuse (verb)	short letter (verb)
accept an excuse for
defend, explain, clear away, or make excuses for by reasoning
excuse, overlook, or make allowances for; be lenient with
serve as a reason or cause or justification of
grant exemption or release to
ask for permission to be released from an engagement