The word 是否 is formed by combining two opposite-meaning characters into a single, fixed compound. The character 是 means "to be" or "yes", representing affirmation, while 否 means "not" or "to negate", representing denial. Their pairing creates a conceptual unit that encapsulates the whole idea of a binary choice or doubt between positive and negative states, merging into a single term meaning "whether or not". This structure is a classic example of Chinese lexical formation through the juxtaposition of direct antonyms to express a unified, abstract concept.