We predict that you will guess the correct origins of "retrodict," and chances are we will not contradict you. English speakers had started using "predict" by at least the early 17th century; it's a word formed by combining "prae-" (meaning "before") and "dicere" (meaning "to say"). Since the rough translation of "predict" is "to say before," it's no surprise that when people in the 1950s wanted a word for "predicting" the past, they created it by combining the prefix for "backward" ("retro-") with the "-dict" of "predict." Other "dicere" descendants in English include "contradict," "benediction," "dictate," "diction," and "dictionary."