The term “original sin” was first brought into the church by Augustine (called into controversy concerning sin by the Pelagians) in order that he might have a certain term to use in his disputes with them. The schools retained it as suitable to express exactly the nature of that sin. It is however so called not by reason of first origin (which man created by God had), but by reason of second origin (which it had from the first parent, but by reasons of its principle [because it is from originating sin] and by reason of the mode of propagation [because it inheres in us from our origin] and by reason of its effects [because it is the origin of actual sins]).
Francis Turretin, Institutes of Elenctic Theology, Ninth Topic, Q. X, IV. (p. 630) (brackets in original).