异性
yìxìng · HSK 7
opposite sex
♀️♂️ 异 different + 性 sex/nature = the different sex, i.e. the opposite sex
异 means different or other; 性 means sex, gender, or nature. Together: a person of the different gender. The science senses (isomerism, metamerism) follow the same logic of different forms sharing one base.
性 — heart radical 忄 + 生 (life/birth)
性 is a semantic-phonetic compound. The heart radical 忄 supplies the meaning, pointing to inner feelings or innate qualities, while 生 ('birth, life') gives the sound and hints at what one is born with. It originally meant 'inborn nature' and later extended to 'character,' 'gender,' and 'sex.'