From a ship’s deck to feeling ill
The nautical explanation begins with a practical change of place. A sailor who felt sick or was worn down by rough conditions could go below deck, out of the wind, rain, and spray. “Under the weather” may have described that position before becoming a way to say someone felt unwell.
Going below could offer shelter, but it could not stop a ship from pitching and rolling. For someone already seasick, the cabin might still feel miserable. The expression’s appeal lies in that image: a person physically beneath the weather, and figuratively feeling its effects.
A phrase that outlasted the voyage
In everyday speech, the idiom no longer requires a ship, bad weather, or even a specific illness. It is a mild, general way to say you are not feeling well—often less dramatic than saying you are sick. The nautical image survives in the wording, even when the person saying it is resting at home.
