There are several synonyms for the phrase "live without benefit of matrimony." Some people might use the phrase "shack up" to describe couples who are living together but aren't officially married. Other synonyms include "cohabitate," "live-in relationship," and "domestic partnership." While some people might view these relationships as less legitimate than traditional marriages, others see them as a natural step in modern relationships. Regardless of how society views these partnerships, they continue to be an increasingly popular choice for couples who want to live together, share expenses, and build a life together without the binding commitment of marriage.