Merriam-Webster Collegiate Dictionary - perineum

 noun  (plural perinea)  Etymology: Middle English, from Late Latin perinaion, from Greek, from peri- + inan to empty out; perhaps akin to Sanskrit i??ati he sets in motion  Date: 15th century an area of tissue that marks externally the approximate boundary of the outlet of the pelvis and gives passage to the urinogenital ducts and rectum; also the area between the anus and the posterior part of the external genitalia  • perineal adjective