Memoir comes from French 'mémoire' (a written account), from Latin 'memoria' (memory), rooted in PIE *(s)mer- (to remember).
A historical account or biography written from personal knowledge or special sources; a written account of one's own life and experiences.
From French 'mémoire' (memory, written account), a specialized use of the masculine form 'le mémoire' (a memorandum, a written record), as distinct from the feminine 'la mémoire' (the faculty of memory). Both derive from Latin 'memoria' (memory, remembrance), from 'memor' (mindful, remembering), from PIE *(s)mer- (to remember, to be mindful, to care for). The PIE root *(s)mer- produced an extraordinary range of descendants: Greek 'mérimna' (care, anxiety — remembering as worrying), Sanskrit