"Flash on" refers to the concept of suddenly remembering or recalling something. There are several synonyms for this phrase, including "come to mind," "occur to," "spring to mind," "strike," "dawn on," and "register." When something "flashes on," it means that the mind has suddenly been triggered to recall something important or relevant. Using synonyms for "flash on" can help make communication more specific and clear. These phrases can be used to express the suddenness and importance of a revelation or realization, making it easier to convey important messages and ideas.