The prefix "lac-" is commonly used in English language to denote something related to milk or dairy products. It can also refer to "lake" or "pond". However, there are many other synonyms for the prefix "lac-" that are less commonly used. Some of these synonyms include "galact-", which means milk, "lactar-", which means to milk, "lacti-", which means containing milk, and "lactal-", which means relating to milk. Other synonyms include "aqu-", which means water, and "natr-", which means relating to streams or springs. Using these synonyms, you can add variety and freshness to your writing while still conveying the same meaning.