There are various synonyms for the phrase "reduce to an absurdity," which essentially means to take an argument or idea to an extreme level to show its flaws. One common synonym is "reductio ad absurdum," which is a Latin term that means the same thing. Another synonym is "extreme case scenario," which is often used in business and law to describe a hypothetical situation taken to the most extreme outcome possible. "Reductio ad absurdum" and "extreme case scenario" are similar in that they both involve taking something to an extreme to demonstrate its weaknesses. Other synonyms for "reduce to an absurdity" include "overemphasis," "overblowing," and "overstating".