gynecomastia n.

also gynaeco-, before a vowel gynec-, word-forming element meaning "woman, female," from Latinized form of Greek gynaiko-, combining form of gynē "woman, female," from PIE root *gwen- "woman." Also see æ (1).

before vowels mast-, word-forming element meaning "female breast, mammary gland," from Greek mastos "woman's breast," from madan "to be wet, to flow," from PIE *mad- "wet, moist, dripping" (source also of Latin madere "be moist;" Albanian mend "suckle;" see mast (n.2)).