Is it ensure, insure, or assure?
"pertaining to the seashore," 1650s, from Latin littoralis "of or belonging to the seashore," from litus (genitive litoris) "seashore" (cf. Lido), of unknown origin, possibly from PIE root *lei- "to flow." The noun is first recorded 1828, from Italian littorale, originally an adjective, from Latin littoralis.
Relating to the coastal zone between the limits of high and low tides. The littoral zone is subject to a wide range of environmental conditions, including high-energy wave action and intermittent periods of flooding and drying along with the associated fluctuations in exposure to solar radiation and extremes of temperature. Compare sublittoral.