The phrase "dawned on" means to realize or understand something gradually. This phrase can be replaced with other synonyms such as "occurred to", "hit upon", "struck", or "became aware of". "Occured to" implies that the realization came upon the person gradually. "Hit upon" is used to suggest that someone has stumbled upon a sudden realization. "Struck" implies that the realization hit with a sudden force. "Became aware of" suggests that the realization has slowly seeped into the person's consciousness. Using different synonyms for "dawned on" can add variety and nuance to your writing.