When it comes to scheduling events or meetings, "pencil in" is a common phrase used to indicate that something is tentatively planned to happen at a certain time. However, there are several synonyms that can be used in place of "pencil in" to convey the same meaning. These include "put down", "jot down", "note down", "mark in", "reserve", "schedule", and "book". Each of these alternative phrases can be used interchangeably with "pencil in" to indicate a preliminary arrangement that may be subject to change in the future. It's important to use clear and precise language when scheduling events to avoid confusion and ensure everyone is on the same page.