The word salary comes from the Latin salarium, simply meaning- salt.
When barters were the only way of commerce, and salt being one of the most important substances, people there, were paid with salt which they could barter for other needed properties.
The word soldier, comes from the same place and is even closer to salt than salary is- the Latin and Italian soldato is made of sol meaning salt, and dat meaning to give. Thus the word soldier actually means “one who is being paid”.