莫须有 is formed by the direct juxtaposition of three characters: 莫 (meaning "not" or "none"), 须 (meaning "must" or "necessary"), and 有 (meaning "have" or "exist"). It originates from a specific historical account where the phrase was used as a complete utterance to dismiss the need for evidence, thus creating a fixed idiom that denotes unfounded accusations through the combined literal meanings of its components in that context.