The phrase "seep in" refers to something gradually penetrating or slowly spreading into something else. Some synonyms for this phrase include "filter in," "infiltrate," "permeate," "penetrate," "creep in," "meander in," "ooze in," and "trickle in." Each of these words implies a slow and steady process of gradually spreading or penetrating into something. "Seep in" is often used in the context of ideas or concepts that slowly become part of one's consciousness or understanding over time. In general, these synonyms reflect a sense of something gradually becoming ingrained or absorbed by another entity.