Sentence:  As well as being greatly useful to <WSD>tractators</WSD> who wanted to go on to further voyages or to stay overseas for a longer period, it was also indispensable when a <WSD>tractator</WSD> fell ill or died. 
Meaning of the word marked with <WSD> tags:  In medieval commerce, the person who handles or transports merchandise on behalf of an investor; an entrepreneur.