1. A reference to anyone or anything that existed or occurred after the Biblical Flood: After the downpour subsided and the ark rested on Mount Ararat, Noah tested the postdiluvian conditions by releasing a raven and then a dove which brought back an olive branch. Seven days later, he sent out another dove that did not return.
2. In geology, relating to a period after deposits of earth, etc. have been produced by a flood: The postdiluvial conditions after the deluge of very heavy rain resulted in significant damage to many homes and other buildings.