The word 异性 is formed by combining two individual characters, each contributing a core meaning to create a new, unified concept. The first character, 异 (yì), carries the fundamental idea of "difference", "other", or "dissimilar". The second character, 性 (xìng), represents the essential notions of "nature", "character", or specifically "sex/gender". When merged, their meanings conceptually fuse, with 性 specifying the category and 异 defining the relationship within it, thus directly forming the idea of "the other/different sex" or "opposite gender".