magniloquent

Magnus means "great" in Latin; loqui is a Latin verb meaning "to speak." Combine the two and you get magniloquus, the Latin predecessor of magniloquent. English-speakers started using magniloquent in the 1600s—even though we have had its synonym grandiloquent since the 1500s. (Grandiloquent comes from Latin grandiloquus, which combines loqui and grandis, another word for "great" in Latin.) Today, these synonyms continue to exist side by side and to be used interchangeably, though grandiloquent is the more common of the two.