1650s (n.) "member of the lowest or poorest class of a community;" 1660s (adj.) "of or belonging to the lowest class of people," hence "mean, vile, vulgar;" with -ian + Latin proletarius "citizen of the lowest class" (as an adjective, "relating to offspring"), from proles "offspring, progeny" (see prolific). In ancient Rome, according to the traditional division of the state, the proletarius was one of the propertyless people, exempted from taxes and military service, who served the state only by having children. The modern political sense of proletarian is by 1851.

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Definitions of proletarian from WordNet

proletarian (n.)
a member of the working class (not necessarily employed);
Synonyms: prole / worker