Meaning In a state of confusion, disoriented, unsure about what to do. Used mostly in British and Australian English. Also simply said as “at sea”.
Origin Gary Martin at ThePhraseFinder says “This is an extension of the nautical phrase ‘at sea’. It dates from the days of sail when accurate navigational aids weren’t available. Any ship that was out of sight of land was in an uncertain position and in danger of becoming lost.
‘At sea’ has been in use since the 18th century, as here, in Sir William Blackstone’s Commentaries on the Laws of England, 1768:
If a court of equity were still at sea, and floated upon the occasional opinion which the judge who happened to preside might entertain of conscience in every particular case.
The earliest reference to ‘all at sea’ in print that I can find is fromTravel and Adventure in South-East Africa, 1893, by Frederick C. Selous:
I was rather surprised to find that he seemed all at sea, and had no one ready to go with me.
‘All at sea’ also means perplexed or bewildered, as in “She was all at sea in these new surroundings.” This idiom transfers the condition of a ship that has lost its bearings to the human mind. Charles Dickens used it in Little Dorrit (1855):
Mrs. Tickit … was so plainly at sea on this part of the case.”
Video Check out Jamie Cullum’s song interpretation with nautical settings in his video, “All At Sea”.