v.1. To cause something to be inserted by repeated or continuous effort: Hold the cloth in one hand and work in the thread using a needle. The dough won't absorb the extra flour unless you work it in by kneading.
2. To insert or make space for something: When I wrote the report, I worked in a request for money. It's an unusual proposal, but I think I can work it in.
3. To make time available for something or someone in an otherwise busy or filled schedule: I know you don't have an appointment, but the doctor will try to work you in.
4. To share equipment at a gymnasium or fitness center with a person who is already using it: He had been using the weight machine for 30 minutes, so I asked if I could work in.