Undersea/ˈʌndərsiː/ Definition 1 of 2Pro Tip 1/3Physical Locale Refers to something physically below sea level, not just related to water. The sunken ship became an undersea habitat for marine life. Pro Tip 2/3Not Above Sea The 'undersea' tag implies the object isn't visible above the sea level. The undersea pipeline is completely hidden from view. Pro Tip 3/3Implies Mystery 'Undersea' carries an aura of the unknown, as much of it remains unexplored. Legends often tell of undersea kingdoms and lost cities.