'Vow' in the Bible

She made a vow and said, “O Lord of hosts, if You will indeed look on the affliction of Your maidservant and remember me, and not forget Your maidservant, but will give Your maidservant a son, then I will give him to the Lord all the days of his life, and a razor shall never come on his head.”

Then the man Elkanah went up with all his household to offer to the Lord the yearly sacrifice and pay his vow.

Jonathan made David vow again because of his love for him, because he loved him as he loved his own life.