Though it sits next to amnesia, an amnesiac is not the illness. It is a person who has amnesia — someone who cannot remember in the usual way. You can also use it as a describing word: an amnesiac patient. The condition is amnesia; the person is an amnesiac. Writers and films like the word. It is medical and a little literary, not an everyday word at the shops.

失憶者、失憶症患者（不是病名本身）