The term 'UM...SURE' can be broken down into three separate crossword solutions: YEAH (4 letters), IGUESS (6 letters), and IGUESSSO (8 letters). YEAH is an informal expression of agreement, often used to show enthusiasm. IGUESS is a more hesitant version of the same expression, suggesting uncertainty or doubt. Finally, IGUESSSO is an even more uncertain version of the expression, implying that the speaker is not sure of their answer.