Freelance workers - very often self-employed writers or musicians - aren't continuously employed by a single company. In medieval times, when knights and lords fought for supremacy, a freelancer was literally a lance soldier for hire. We now use "mercenary" to mean that. The term freelancer passed into modern English language as late as 1820 when Sir Walter Scott included in his novel Ivanhoe the line "Ivanhoe offers Richard the services of my Free Lancers".