Why is the ninth month called September?
"loss of memory," 1786 (as a Greek word in English from 1670s), Modern Latin, coined from Greek amnesia "forgetfulness," from a-, privative prefix, "not" (see a- (3)) + mimneskesthai "to recall, cause to remember," a reduplicated form related to Greek mnemnon "mindful," mneme "memory," mnasthai "to remember;" from PIE root *men- "to think, remember" (see mind (n.)).
amnesia am·ne·sia (ām-nē'zhə)
The loss or impairment of memory.
A loss of memory, especially one brought on by some distressing or shocking experience.
Note: A common variant is selective amnesia; the term is applied to public officials who, when questioned about alleged wrongdoing, profess that they cannot remember.