Other forms: dawned; dawning; dawns
The noun dawn refers to the first light of day, or the first time period, like the dawn of a new era, which occurs when a new president takes office.
Not just the beginning of a day, the noun dawn can refer to any beginning, like the dawn of the Internet era. As a verb, dawn can mean "become light" or "become clear," like when it dawns on you that you left an important paper at home today. In that case, you can suddenly see what you did wrong, like at the dawn of a new day, when it is no longer dark and you can see, literally.