Beginning with the word which has served to designate the fact, ‘caste’ is of Portuguese and Spanish origin: ‘casta, properly something not mixed, from the Latin castus, chaste’ (Littré’s Dictionary). The word seems to have been used in the sense of race by the Spaniards, and to have been applied to India by the Portuguese in the middle of the fifteenth century. lb In English, there is a use (cast) in the sense of race in 1555, and the Indian sense is encountered at the beginning of the seventeenth century; the French spelling, caste, is scarcely found before 1800. In French, Littré records that the word was only inserted in the Dictionary of the Academy in 1740 and appears neither in Furetière nor Richelet. It was used in the technical sense at least from 1700 (Dumont 21).
Dumont, Louis. “History of Ideas.“ Homo Hierarchicus: The Caste System and Its Implications, Translated by Mark Sainsbury, University of Chicago Press, 1970, pp. 21-32.