Salary

Salary goes back to the Latin word that originally denoted a 'allowance given to a Roman soldier for buying salt' This was 'Salarium,' a derivative of sal, 'salt.' Salt being in former times a valued commodity over which wars were fought, rather that taken for granted as it is today. It soon broadened out to mean 'fixed periodic payment for work done,' and passed in this sense via Anglo-Norman salarie into English

Source: Dictionary of Word Origins, John Ayto