Merriam-Webster Collegiate Dictionary - lordosis

 noun  (plural lordoses)  Etymology: New Latin, from Greek lordosis, from lordos curving forward; akin to Old English belyrtan to deceive  Date: 1704  1. abnormally increased inward curvature of the lower region of the spine resulting in a concave back as viewed from the side — compare kyphosis  2. a mating posture of some sexually receptive female mammals (as rats) in which the head and rump are raised and the back is arched downward  • lordotic adjective