1. an unprincipled person (often used humorously or affectionately). 2. (especially in Calvinism) a sinner who is not of the elect and is predestined to damnation. 1. unprincipled (often used as a humorous or affectionate reproach): a long-missed old reprobate drinking comrade 2. (in Calvinism) predestined to damnation.