reminder vs memento

reminder and memento both are nouns.

Word	Noun	Adjective	Verb	Adverb
reminder	Yes	No	No	No
memento	Yes	No	No	No

As nouns, memento is a hyponym of reminder; that is, memento is a word with a more specific, narrower meaning than reminder:

Other hyponyms of reminder include deja vu, souvenir, memento mori, shades.

reminder (noun)	memento (noun)
an experience that causes you to remember something	a reminder of past events
a message that helps you remember something
someone who gives a warning so that a mistake can be avoided