The word "勤勤恳恳" is formed through the reduplication of the two characters "勤" and "恳", arranged in an AABB pattern where "勤" is repeated as "勤勤" and "恳" as "恳恳". This structural repetition intensifies the individual meanings of "勤" (diligent) and "恳" (earnest), resulting in a compound term that conveys a heightened sense of devoted and conscientious effort.