time of day when light first appears; daybreak 黎明; 破晓; 拂晓: We must start at dawn. 我们必须天一亮就启程. * He works from dawn till dusk. 他从天亮工作到天黑. * It's almost dawn. 天差不多要亮了. 
(fig 比喻) beginning; first signs of sth 开始; 开端; 发端: the dawn of hope, love, intelligence, civilization 希望﹑ 爱情﹑ 智力﹑ 文明的开端 * the dawn of a new age 新时代的曙光. 
(idm 习语) the crack of dawn => crack1.# ,dawn `chorus sound of birds singing in the early morning 清晨的鸟啼声.