Proselytize comes from the noun proselyte (meaning "a new convert"), which comes from the Late Latin noun proselytus. Proselytus means "stranger" or "alien resident," and comes from a similar Greek word (prosēlytos). When proselytize entered English in the 17th century, it had a distinctly religious connotation and meant simply "to recruit religious converts." This meaning is still common, but today one can also proselytize in a broader sense - recruiting converts to one's political party or pet cause, for example.