Pencil

1. To write or mark with a pencil; to paint or to draw.
   
pencil in
to write (a tentative appoinment) on an appointment calendar, so as to reserve time, but to allow the appointment to be readily canceled and replaced with another; -- also used figuratively, with other means of recording appointments. The notion being that something written in pencil can be more easily changed than something written in ink. The phrase is commonly used in the early stages of organizing a meeting of multiple persons, before it is known whether all attendees will be free at the suggested time.