The term 'most underhanded' can be described by the crossword solutions sliest, LOWEST, dirtiest, and slyest. Sliest means to be the most cunning or crafty, while LOWEST implies the least honorable or ethical. Dirtiest suggests the most immoral or corrupt, and slyest implies the most cunning or wily. All of these words are related to the idea of being the most underhanded, meaning the most deceitful or unscrupulous.