As a Verb or Adjective: 1. Of a secret or a piece of information, to not tell anyone about it. English = keep mum, (be) mum. 2. To communicate without using any or very few lip patterns or facial expressions, usually when you are signing. 3. To keep quiet, especially when suffering pain or discomfort; to not complain. Note: 1. Can also be made with only the index and thumb extended (7 or L handshape) which close next to the mouth.