Summary: に違いない (ni chigainai) is a phrase that is derived from the verb 違う (chigau), “to be different” or “to vary.” 違いない is a negative form of 違う that means the opposite, to be “sure,” “unmistaken,” or “certain.” に違いない at the end of the sentence conveys the feeling of the English “certainly,” “definitely,” and “surely.
