PARTICIPATE%2C SHARE(4 letters) The crossword solutions for the term BE IN ON are KNOW and SHARE. To be in on something means to have knowledge of or to be involved in something, usually a secret or confidential matter. It can also mean to be included in a plan or activity, or to be part of a group that is aware of something. To KNOW something is to have information or understanding about it, while to SHARE something is to give a portion of it to someone else.