1. relax; become less active
need to calm down
To 'calm down' is the process of becoming more relaxed or less emotional. This is a phrasal verb usually used for encouraging others to behave in a less emotional way. You can ask other people to calm down or inform them that you need time to become calmer. This is a popular phrasal verb you will hear used in social and professional situations. Phrases with a similar meaning include 'relax' 'remain calm' and 'don't lose the head.