As a Noun: 1. Your ability to think, including all the thoughts that you have. English = mind. As a Verb or Adjective: 1. To be related to the processes of thinking or to intelligence, rather than to simple physical processes. English = (be) mental. 2. To talk or behave in a strange or foolish way because of stupidity, mental retardation or mental illness. English = (be) crazy, (be) silly, (be) mental.