v.1. To insert or introduce something into the course of an activity, performance, or conversation: The lawyer threw in a few snide comments while we conversed. The team threw in a new goalie halfway through the game. Let me throw my two cents in.
2. To add some extra thing or amount with no additional charge: If you order within the next 15 minutes, we'll throw in a book bag. The car salesperson threw the snow tires in for free.
3. To engage something, such as a clutch: He threw in the clutch and drove off. Be careful not to stall when you throw it in.