When someone is said to be feeling
under the weather they are suffering from a mild
illness and don't feel "100%".
There are two schools of thought as to the
origins of this
idiom:
- The phrase is an abbreviated form of "under the influence of the weather". This is an
allusion to the theory that changes in weather are often linked to the onset of
ailments such as influenza and the common cold.
- The phrase has naval origins: Bad weather would often cause sailors to feel
seasickness.
An alternative theory along the same nautical lines is that seasick sailors
would be sent below deck, or "under the weather", to recover. Anyone who has sailed knows
that this may not be the best course of action as fixing your eyes on the horizon is a
good way to counteract the effect of a rolling deck. Also, being "topside" means it's a
lot easier to clean up after vomitting.