Admit it, you've always wondered what is the adjectival form of amnesia. And you don't get to claim that you once knew it but forgot -- that would be too meta, at least for this word. I don't know when this one sprung into being, but it had to have been after 1786, when amnesia was coined in Neo-Latin from Greek root amnesia, forgetfulness, from a-, not + mimneskesthai, to recall, to cause to remember. Note that, like many English adjectives, it can also be a noun -- something that causes amnesia:
Anterograde amnesia can be caused by amnestics such as benzodiazepines or alcohol, which prevent experiences from being transferred from temporary to permanent memory storage.
(Okay, lame usage example, but it's the best I got this morning.)