Interlineating refers to the process of adding lines between existing lines of written or printed text. However, there are several synonyms for this word that can be used interchangeably. One of the most common synonyms is "inserting," which implies adding something in between what already exists. Another synonym is "interposing," which means to place between two other things. "Interspersing" can also be used to convey the same meaning, as it means to scatter or spread among other things. Finally, "intercalating" can be used as a synonym, which has a more scientific connotation, as it refers to adding an extra layer between two existing layers.