Late 16th century; earliest use found in Thomas Rogers (c1553–1616), religious controversialist and Church of England clergyman. From classical Latin prōlētārius (adjective) belonging to the lowest class of citizens, common, vulgar, (as noun) Roman citizen of the lowest class, person who served the state not with his property but only with his offspring, probably from prōlēs + -ārius, with inserted -t- (probably on the model of adjectives in -tārius, as elementārius, voluntārius).