late 14c., "memorable, excellent," also "remembered, committed to memory," from Old French memorial "mindful of, remembering" (Modern French mémorial), and directly from Latin memorialis "of or belonging to memory," from memoria "memory" (from PIE root *(s)mer- (1) "to remember"). From mid-15c. as "preservative of memory, serving for commemoration."
A Middle English word for "having to do with memory" was memorative (late 14c.), from Old French memoratif, from Latin memorativus. Though useful, it apparently has not survived.
late 14c., "fame, renown, reputation," also "a commemorative gesture, monument, or rite;" in general, "something by which the memory of a person, thing, or event is preserved," from Old French memorial "record, report," and directly from Late Latin memoriale "a memorial," noun use of neuter of Latin memorialis (adj.) "of or belonging to memory," from memoria "memory" (from PIE root *(s)mer- (1) "to remember").
Meaning "memorial act, commemorative gesture, monument, etc.," is from late 14c., as is the sense of "a written representation of facts made to a legislative or other body as the grounds for a petition." Related: Memorialist.