The antonyms for underwritten include "overwritten," "abundant," "excessive," "surplus," and "superfluous." These words indicate a condition in which there is more than what is strictly necessary or required. Overwritten refers to something that has been written too much, while abundant implies a plentiful or copious supply of something. Excessive and surplus are interchangeable and suggest more than is needed. Superfluous is often used to describe something that is unnecessary or redundant. In contrast to underwritten, these antonyms suggest a state of excess or unnecessary abundance.