Jewish, English, Welsh, French, etc.: from the Biblical Hebrew personal name yishāq ‘he laughs’. This was the name of the son of Abraham (Genesis 21:3) by his wife Sarah. The traditional explanation of the name is that Abraham and Sarah laughed with joy at the birth of a son to them in their old age, but a more plausible explanation is that the name originally meant ‘may God laugh’, i.e. ‘smile on him’. Like Abraham, this name has always been immensely popular among Jews, but was also widely used in medieval Europe among Christians. Hence it is the surname of many gentile families as well as Jews. In England and Wales it was one of the Old Testament names that were particularly popular among Nonconformists in the 17th–19th centuries, which accounts for its frequency as a Welsh surname. (Welsh surnames were generally formed much later than English ones.) In eastern Europe the personal name in its various vernacular forms was popular in Orthodox (Russian, Ukrainian, and Bulgarian), Catholic (Polish), and Protestant (Czech) Churches. It was borne by a 5th-century father of the Armenian Church and by a Spanish saint martyred by the Moorish rulers of Cordoba in AD 851 on account of his polemics against Islam. In this spelling, the American family name has also absorbed cognates from other European languages, e.g. German Isaak, Dutch Izaac, etc. (for the forms, see Hanks and Hodges 1988). It is found as a personal name among Christians in India, and in the U.S. is used as a family name among families from southern India.