Meaning: If you join in an activity, you start doing it with people who are already doing it.Synonym: take part, participate
- join in Barry's friends were playing cards when he arrived, so he pulled up a chair and joined in.
- join in sth When I came in, my friends were talking. After listening for a while, I joined in the discussion and told them what I thought.
join in: discussion, conversation, game, fight
When Tom saw his friends fighting some other boys, he joined in and