c. 1200, dauen, "to become day, grow light in the morning," shortened or back-formed from dauinge, dauing "period between darkness and sunrise," (c. 1200), from Old English dagung, from dagian "to become day," from Proto-Germanic *dagaz "day" (source also of German tagen "to dawn"), from PIE root *agh- "a day." Probably influenced by Scandinavian cognates (Danish dagning, Old Norse dagan "a dawning"). Related: Dawned; dawning.
Figurative sense "begin to develop" is from 1717. Of ideas, etc., "begin to become apparent or evident to the mind," by 1852.