As a Noun: 1. A person who has a very great natural ability and talent, especially for a particular subject or activity; a person who is very clever indeed. English = genius. 2. A very great ability or skill in something. English = genius, intellect. As a Verb or Adjective: 1. To have a very great natural ability and talent, especially for a particular subject or activity; to be very clever. English = (be) brilliant. Informal English = (be) brainy.