Is it ensure, insure, or assure?
seabird, 1670s, pitteral, modern spelling first recorded 1703 by English explorer William Dampier (1651-1715), who wrote the bird was so called from its way of flying with its feet just skimming the surface of the water, which recalls the apostle's walk on the sea of Galilee (Matt. xiv:28); if so, it likely was formed in English as a diminutive of Peter (Late Latin Petrus). If this is folk etymology, the true source of the name is undiscovered. French pétrel (1760) probably is from English.