'Solemn' in the Bible

"The Lord, the God of heaven, who took me from my father's house and the land of my relatives, promised me with a solemn oath, 'To your descendants I will give this land.' He will send his angel before you so that you may find a wife for my son from there.

So the servant placed his hand under the thigh of his master Abraham and gave his solemn promise he would carry out his wishes.

Stay in this land. Then I will be with you and will bless you, for I will give all these lands to you and to your descendants, and I will fulfill the solemn promise I made to your father Abraham.