spon·dy·lo·lis·the·sis 
(spŏn′dl-ō-lĭs-thēsĭs)
(spŏn′dl-ō-lĭs-thēsĭs)n.
Forward displacement of one of the lower lumbar vertebrae over the vertebra below it or on the sacrum.
[New Latin spondylolisthēsis : Greek spondulos, vertebra + Greek olisthēsis, dislocation, slipping (from olisthanein, to slip).]