Three pieces: 睾 (gāo, 'testis' - from 睾丸), 甾 (zāi, 'steroid' - a chemistry term coined to fit the four-fused-ring structure), 酮 (tóng, 'ketone'). Literally 'testis-steroid-ketone' - a precise structural description of the molecule.
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睾酮 (gāotóng) is the more common everyday/medical name (drops the 甾). 睾甾酮 is the fuller, more technical chemistry-textbook form. 睾丸激素 (gāowán jīsù, 'testicular hormone') also appears in popular health writing.
