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.
Top 血 - a vessel with a drop of blood above its rim, used as a graphic stand-in for an enclosed organ. The modern shape reads as 血, lending an anatomical, fluid-filled flavour fitting for an internal body part. Indexed under Kangxi #109 目 (mù) by tradition; no visible 目-element survives in the modern silhouette.
Bottom 幸 carries the phonetic role - xìng drifting to gāo through historical sound change. A similar phonetic-shape appears in 报 and in 译 with a different reading. Purely phonetic in 睾; the 'fortunate' meaning doesn't carry over.
Filed under radical 目 (mù, #109) by convention. 目 is not a separate component in 睾, so no strokes are highlighted.
