Hadst a flash is an old English expression that means to have a sudden realization or moment of insight. There are many alternative ways to express this concept such as epiphany, revelation, enlightenment, awakening, and illumination. These synonyms all convey the idea of suddenly understanding something in a profound way. Whether experienced during an A-ha moment or while being struck by the proverbial lightning bolt, these phrases capture the essence of a sudden mental breakthrough. So, instead of saying "hadst a flash" next time, consider using one of these synonyms to add color and variety to your language.