"Black friar, one of an order of mendicant preaching friars," 1630s, from Latin form of the name of Domingo de Guzman (Santo Domingo), who founded the order in Languedoc. They were confirmed by the pope in 1216. His name, like Italian form Dominic (q.v.), is from Latin dominicus,which in Christian use meant "devoted to the Lord."
"native or inhabitant of the Dominican Republic," 1853, from the name of the republic, which became independent from Haiti in 1844; formerly it was Santo Domingo, the name of the capital and of the European colony established there in 1494, which was named for Santo Domingo de Guzmán, founder of the Order of the Dominicans, who established a presence there (see Dominican (1)).
1826, "native or inhabitant of the Caribbean island of Dominica," which was named by Columbus for Latin (dies) dominica "Sunday," the day of the week on which he spotted it (Nov. 3, 1493) on his second voyage. From Latin dominicus "pertaining to a lord," in Christian use, "pertaining to the Lord," from dominus "lord, master," from domus "house" (from PIE root *dem- "house, household").