Definition from Wiktionary, the free dictionary
- A keepsake; an object kept as a reminder of a place or event.
- I kept the shell as a memento of my visit to the seashore.
- 2011 December 16, Denis Campbell, “Hospital staff 'lack skills to cope with dementia patients'”, Guardian:
- Many hospitals have not taken simple steps to lessen the distress and confusion which dementia sufferers' often feel on being somewhere so unfamiliar – such as making signs large and easy to read, using colour schemes to help patients find their way around unfamiliar wards and not putting family mementoes such as photographs nearby.
Usage notes 
- The alternate spelling momento is so common, some references now no longer consider it a misspelling.
- “memento” in Dictionary.com Unabridged, v1.0.1, Lexico Publishing Group, 2006. (usage note)
- second-person singular future active imperative of meminī - remember!