Memoir, or pl. Memoirs, n.
Etymology: [F. mémoire, m., memorandum, fr. mémoire, f., memory, L. memoria. See Memory.]
1. A memorial account; a history composed from personal experience and memory; an account of transactions or events (usually written in familiar style) as they are remembered by the writer. See History, 2.
2. A memorial of any individual; a biography; often, a biography written without special regard to method and completeness.
3. An account of something deemed noteworthy; an essay; a record of investigations of any subject; the journals and proceedings of a society.
Shades of meaning
Fernald has no entry of its own for memoir; he lists it under history.
He lists it without comment; the entries above explain its neighbors.