The phrase "causa causan" refers to a cause that causes something. Synonyms for this phrase include "root cause," "underlying cause," "precipitating factor," and "trigger." These words can all replace "causa causan" in various contexts. For example, if we are discussing the cause of an illness, we might say that the root cause was a viral infection, or the underlying cause was a weakened immune system. Similarly, we might talk about the precipitating factors that led to a particular event, or the trigger that set off a chain reaction of events. By using synonyms for "causa causan," we can help clarify our meaning and make our writing more precise.