Things that have something to do with the ocean are oceanic. Oceanic water comes from the sea, and oceanic study focuses on creatures that live in the ocean and other ocean-related topics.
An oceanic vessel is a fancy way of referring to a ship that sails on the sea, and oceanic tides are the constantly rising and falling levels of ocean water. You can also use this adjective to mean, "as enormous as the ocean," like an oceanic success or an oceanic pile of work to do before the end of the day. Oceanic comes from the Greek okeanos, which in ancient Greece referred to an imagined "endless river surrounding the land."