The term 'round out' can be defined as to complete or supplement something, and the crossword solution for this term is 'COMPLEMENT'. COMPLEMENT is a verb that means to add something to make a whole, or to make something more complete. It is often used in the context of adding something to a group or set to make it more complete. For example, if you have a set of four chairs, you could COMPLEMENT it with a table to make it a complete dining set.