There are a plethora of synonyms for the word "slow in," all of which connote a sense of slowness or delay. Some common alternatives include "gradual," "leisurely," "unhurried," "languid," "protracted," "deliberate," and "tardy." Other substitutes might include "lagging," "dawdling," "stalling" or "dragging." It's important to consider context when selecting the right synonym, as each word may be more suitable for certain uses than others. Whether you're describing the pace of a process or the movement of a person, there's sure to be a synonym for "slow in" that can capture the exact tone and meaning you're looking for.