n.1. The continuous body of salt water covering most of the earth's surface, especially this body regarded as a geophysical entity distinct from earth and sky.
2. a. A tract of water within an ocean.
b. A relatively large body of salt water completely or partially enclosed by land.
c. A relatively large landlocked body of fresh water.
3. a. The condition of the ocean's surface with regard to its course, flow, swell, or turbulence: a rising sea; choppy seas.
b. A wave or swell, especially a large one: a 40-foot sea that broke over the stern.
4. Something that suggests the ocean in its overwhelming sweep or vastness: a sea of controversy.
5. Seafaring as a way of life.
6. Astronomy A lunar mare.
at sea1. On the sea, especially on a sea voyage.
2. In a state of confusion or perplexity; at a loss.