When the moon is still hanging in the sky and the sun is not out yet, a man begins to work hard. 夙 on the oracle bone script reflects this scene to express the meaning of “morning”.
夙 is a compound ideographic character. In the clerical script, the pictographic part of the working man was changed to semi-enclosed structure 
and the Moon was written as 夕.
As “宿”and “夙” have the same pronunciation and similar meaning, such words as “夙敌” and“宿敌”,“夙愿” and“宿愿”, etc used to be interchangeably used.
From the original meaning of 夙, the following meanings were extended:
1.old; former, original
2.inborn; inherited