As a Noun: 1. [Especially when made with two hands] a chronic or persistent brain disease that causes memory loss, personality changes, and difficulty in reasoning (thinking). English = dementia. As a Verb or Adjective: 1. To completely forget to do something that you should have remembered. 2. To be unable to remember things you have learnt (such as your part in a play, or information for an exam) or to be unable to think of anything to say. English = go blank. 3. [Especially when made with two hands] to suffer from a chronic or persistent brain disease that causes memory loss, personality changes, and difficulty in reasoning (thinking). English = have dementia, suffer from dementia.