memorandum (n.)

mid-15c., "(something) to be remembered," a note of something to be remembered for future reference or consideration, from Latin memorandum "(thing) to be remembered," neuter singular of memorandus "worthy of remembrance, noteworthy," gerundive of memorare "to call to mind," from memor "mindful of" (from PIE root *(s)mer- (1) "to remember").

"Used originally as mere Latin, and usually abbreviated mem., to introduce a note of a thing to be done" [Century Dictionary]; by 1540s it came to mean the note itself. The Latin plural is memoranda. Compare also agenda.