A long time ago, in this galaxy, near-primordial savages across parts of Eurasia were using the word men to describe the action of "thinking". This Proto-Indo-European term went into Ancient Greek as mnestis, which changed slightly, semantically, as it took on a meaning of "remembering". This may seem familiar, because when added to the prefix a- ("not"), the word becomes amnestos, or "forgotten". This is connected to the word amnesty through Latin amnestia and French amnestie, and makes sense because in an amnesty the past crimes of a person are forgiven by whoever is doing the pardoning. Meanwhile, the Greeks made the word amnesia, also from the a- prefix and a conjugated form of mnestis, to create a word that meant something more along the lines of "forgetting" than "forgotten". Amnesty entered English two hundred years before amnesia.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd