Undergirt is a verb meaning to support something from underneath. Some synonyms for this word include underpin, reinforce, strengthen, brace, and shore up. These words share the similar meaning of providing support or stability to something that may be in danger of collapsing or falling apart. While undergirt may be considered a lesser-known word, other words with similar connotations such as buttress, bolster, and prop-up are more commonly used. No matter which word is preferred, the ultimate goal is to maintain the integrity and safety of the object or structure being supported.