Deshi is a Japanese word, but it is also used in English. Often, people define deshi as a student, but that does not truly encompass the true meaning of deshi. Deshi means a disciple, a reverent follower, an apprentice, the disciple of the sensei (master). An uchideshi has a far stronger and more personal mentor-protege relationship with the sensei.
Sen-shi was the youngest uchideshi at the dojo: his hard work, great respect for his sensei, and his honor had earned him this position.