Mammoth Uncensored Word List:
16 words ending with my, 15 letters long

archeoastronomy autosplenectomy cholecystectomy cholecystostomy choledochostomy cystolithectomy enterolithotomy fibromyomectomy hemilaminectomy hemispherectomy lymphadenectomy nephrolithotomy pericardiectomy postpolypectomy proctocolectomy ventriculostomy