What does the word "salary" ultimately derive from?

"Salary" is right because it traces back to the Latin salarium, itself connected to sal, the Latin word for salt. Salt was a precious, heavily traded commodity in the ancient world, used for preserving food long before refrigeration, and the word for a Roman soldier's wage carried that association forward into the English word we still use for a paycheck today.

The Latin words for silver (argentum) and labor (labor) are unrelated to salarium's etymology, even though both concepts — being paid, and working — are naturally tied up in the meaning of a salary; the actual linguistic root points specifically to salt, not to any other valuable substance or to the idea of work itself.

Salt's value shows up in other everyday words too: "salad" comes from the Roman habit of salting vegetables, and the phrase "worth one's salt" still means someone is doing a good, valuable job.