The base of the adjective “sagacious” is “sage,” which can be used as both a noun and an adjective. Use “sage” as an adjective meaning “wise,” or as a noun for “a wise person.” Pull out the adjective “sagacious” if you think it’s wise to use a fancier word. It’s almost synonymous with “sage,” but there’s a slight nuance. To be sagacious is to be wise, but specifically by showing keen judgment. It’s not just about intelligence; it’s showing discernment, too.