The word "most piggyback" can be replaced by a variety of synonyms that convey the same meaning. Some alternatives include "heaviest load," "greatest burden," "biggest weight," "largest responsibility," and "most weighty task." Each of these words highlights the idea of carrying a heavy load, either figuratively or literally. They can be applied to situations where someone is responsible for carrying the majority of the work or burden, such as a team leader in a project or a caregiver in a family. By using alternative words to describe the concept of "most piggyback," writers can vary their language and add interest to their writing.