Is it ensure, insure, or assure?
also Keltic, 1650s, of archaeology or history, from French Celtique or Latin Celticus "pertaining to the Celts" (see Celt). In reference to languages, from 1707; of other qualities, 19c. The Boston basketball team was founded 1946. Celtic twilight is from Yeats's name for his collection of adapted Irish folk tales (1893).