Is it ensure, insure, or assure?
1814, from grape + fruit. So called because it grows in clusters. The fruit itself was known since 1693 (in Hans Sloane's catalogue of Jamaican plants); presumably it originated there from chance hybrids between other cultivated citrus. It was known by various names before the current one emerged. An ornamental plant chiefly at first, not much eaten until late 19c.