At one time soldiers in ancient Rome were paid, in part,
with a ration of salt called a solarium, from the Latin word
sal (which means salt). If a soldier's performance was not up to
standard, that soldier was said to be "not worth his salt."

Later, when salt was replaced with an actual money allowance
to buy the salt, the allowance itself was called a solarium.
Eventually, solarium came to mean the wages themselves,
and this led to our calling one's pay a salary.

When you can see it coming, duck!