Synonyms for Retral (same or very similar meaning)
WordNet sense 1 (moving or directed or tending in a backward direction or contrary to a previous direction):
retrogradeWordNet sense 2 (directed or facing toward the back or rear):
backwardWordNet sense 3 (at or near the hind end in quadrupeds or toward the spine in primates):
posteriorFrom the ODE community, based on WordNetadd/edit