绝无仅有 is formed by combining the characters 绝 (absolutely), 无 (without), 仅 (only), and 有 (have) into a fixed four-character phrase. The first two characters, 绝无, emphasize absolute absence, while the latter two, 仅有, highlight singular existence, creating a contrast that conveys the meaning of something being so unique that it is the only one of its kind without any equal.