Is it ensure, insure, or assure?
1590s, earlier yland (c.1300), from Old English igland "island," from ieg "island" (from Proto-Germanic *aujo "thing on the water," from PIE *akwa- "water;" see aqua-) + land "land." Spelling modified 15c. by association with similar but unrelated isle. An Old English cognate was ealand "river-land, watered place, meadow by a river." In place names, Old English ieg is often used of "slightly raised dry ground offering settlement sites in areas surrounded by marsh or subject to flooding" [Cambridge Dictionary of English Place-Names]. Related: Islander.
island is·land (ī'lənd)
An isolated tissue or group of cells that is separated from the surrounding tissues by a groove or is marked by a difference in structure or function.
(Heb. 'i, "dry land," as opposed to water) occurs in its usual signification (Isa. 42:4, 10, 12, 15, comp. Jer. 47:4), but more frequently simply denotes a maritime region or sea-coast (Isa. 20:6, R.V.," coastland;" 23:2, 6; Jer. 2:10; Ezek. 27:6, 7). (See CHITTIM.) The shores of the Mediterranean are called the "islands of the sea" (Isa. 11:11), or the "isles of the Gentiles" (Gen. 10:5), and sometimes simply "isles" (Ps. 72:10); Ezek. 26:15, 18; 27:3, 35; Dan. 11:18).