v.1. To write something in with a pencil: The assistant penciled in the editorial changes on the manuscript. After the teacher reviewed my test, I penciled the corrections in.
2. To schedule something tentatively: The secretary penciled in a staff meeting for 3:00. The band penciled a rehearsal in on Friday.
3. To schedule a tentative appointment with someone: We penciled him in for lunch next Monday. The interviewers penciled in the applicant for the end of the week.