gynaecomastia
noun [ U ] medical specialized (US gynecomastia) uk/ˌɡaɪ.nɪ.kəʊˈmæst.i.ə/ us/ˌɡaɪ.nə.koʊˈmæs.ti.ə/
男性乳腺发育，男性乳房发育
the development of breast tissue in men
Gynaecomastia is usually harmless but emotionally upsetting. 男性乳房发育一般来说无害，但是令人恼火。