v.1. To submit something, especially by mail or by electronic means: Let's send in a donation this year. I sent my application for college in by e-mail.
2. To order someone or some group into a place: Will you please send in the next candidate on your way out of the office? They sent me in the garage to fetch a hammer.
3. To have someone enter or reenter a contest, conflict, or situation: The coach is sending in the kicker. The president sent troops in to suppress the riots.