A person who has amnesia or has lost their memory, especially severely.
From Greek 'amnesia' (a- meaning without, mnesis meaning memory) plus '-iac' (a suffix meaning one who is afflicted with). Amnesia itself is a medical term from the 19th century.
The suffix '-iac' is the same one in 'maniac' or 'insomniac'—it marks someone as being in a state or condition, and interestingly, it often carries a hint of pathology or abnormality, showing how suffixes encode attitudes.
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