1812 (n.) "a follower of English economist Thomas R. Malthus (1766-1835)," especially with regard to the doctrines set forth in his "Essay on the Principle of Population" (published anonymously in 1798).
In this work he first made prominent the fact that population, unless hindered by positive checks, as wars, famines, etc., or by preventive checks, as social customs that prevent early marriage, tends to increase at a higher rate than the means of subsistence can, under the most favorable circumstances, be made to increase. As a remedy he advocated the principle that society should aim to diminish the sum of vice and misery, and check the growth of population, by the discouragement of early and improvident marriages, and by the practice of moral self-restraint. [Century Dictionary]
As an adjective, "of or pertaining to Malthus," by 1818. Related: Malthusianism "theory of the relation of population to the means of subsistence" (1825).