1. An object or item that serves to remind one of a person, past event, etc.; keepsake; souvenir
2. Anything serving as a reminder or warning
3. Initial capital letters, italics: Roman Catholic Church: Either of two prayers in the canon of the mass, one for persons living and the other for persons dead
Memento dates to the 1400's and is taken from 'Palm cxxxi of the Canon of the Mass.' It is the from the first word in the canon, which was in Latin. The canon talks specifically about remembering and commemorating the dead, but Latin memento more broadly means "remember." It is the imperative of meminisse ("to remember"), which is a reduplicated form related to mens ("mind"). In English, the meaning "reminder, warning" dates to the 1580's and "keepsake" is first attested in 1768.
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