when did the term "freethinkers" get traded in?

My father was a Socialist and a freethinker, but he went to shul every Friday night and Saturday and attended synagogue on every holiday and every ceremonial. Once when I chided him about his piety in view of the fact that he was a freethinker, he answered me, "These people are my brethren, they are the people among whom I was raised, and I love them. Dudja Silverberg [a very pious Jew] goes to shul to speak with G-d, I go to shul to speak with Dudja."

-Isaac Metzker in A Bintel Brief.