deep-sea \ˈ ̷ ̷| ̷ ̷\adjective Etymology:deep (I) + sea 1.: of, relating to, occurring in, or for use in the deeper parts of the ocean < deep-sea currents > < deep-sea fishes > < a deep-sea line > 2.: acting (as by sailing or fishing) or for use in parts of the oceans far from land < deep-sea fishermen > < a deep-sea tug > — sometimes distinguished from coastal, longshore