The term 'KIND OF RIVERBOAT' can be answered with the three letter word 'TUG'. A TUG is a type of riverboat that is used to move other vessels by pushing or towing them. Tugs are typically smaller than other types of riverboats and are used for a variety of tasks such as towing barges, assisting ships in docking, and providing emergency assistance. They are also used to transport goods and materials along rivers.