Bound form — almost never appears alone. Lives in 睾丸 (gāowán, 'testicle' lit. 'testis-pellet'), 睾酮 (gāotóng, 'testosterone'), 隐睾 (yǐngāo, 'undescended testicle'). Medical/biology register.
mistakes
Easy to misread as 皋 (gāo, 'shore; mound') — almost identical shape, but 睾 contains 目 ('eye') at the top while 皋 has 白. Same pinyin, very different meanings.
