The phrase "on sea" can be used in various contexts, referring to activities, locations, or situations related to the sea or maritime environment. Some synonyms for "on sea" may include "at sea," "on board," "afloat," "sailing," "navigating," "cruising," "voyaging," "traversing," "seafaring," or "marine." These terms suggest a sense of movement or action, emphasizing the dynamic and fluid nature of sea-related activities. They may also connote a sense of adventure, exploration, or discovery, evoking the allure and mystery of the vast ocean. Whether you are a sailor, fisherman, traveler, or simply a curious observer, using these synonyms can add richness and depth to your language and expression.