Adenomyosis uteri: Also known more succinctly as adenomyosis (pronounced ad-den-o-mi-o- sis), this is a common benign condition of the uterus in which the endometrium (the mucous membrane lining the inside of the uterus) grows into the myometrium (the uterine musculature located just outside the endometrium) The endometrium and myometrium under normal circumstances live adjacent to one another as discrete neighbors. In adenomyosis, the endometrium invades the myometrium. The myometrium may respond to this intrusion with muscular overgrowth. If an island of endometrial tissue is contained and circumscribed within the myometrium, it forms a nodule called an adenomyoma (plural: adenomyomata). Adenomyosis is made up of adeno (gland) + myo (muscle) +osis (a condition of) = a condition of glandular tissue (referring to the endometrium) in the muscle (the myometrium). Adenomyosis goes by several other names including endometriosis interna or uterina, and adenomyometritis.