History And Origin
English: from the female personal name Isabel(l)(a). This originated as a variant of Elizabeth, a name which owed its popularity in medieval Europe to the fact that it was borne by John the Baptist's mother. The original form of the name was Hebrew Elisheva ‘my God (is my) oath'; it appears thus in Exodus 6:23 as the name of Aaron's wife. By New Testament times the second element had been altered to Hebrew shabat ‘rest', ‘Sabbath'. The form Isabella originated in Spain, the initial syllable being detached because of its resemblance to the definite article el, and the final one being assimilated to the characteristic Spanish feminine ending -ella. The name in this form was introduced to France in the 13th century, being borne by a sister of St. Louis who lived as a nun after declining marriage with the Holy Roman Emperor. Thence it was taken to England, where it achieved considerable popularity as an independent personal name alongside its doublet Elizabeth.
Dictionary of American Family Names, Oxford University Press, Inc. © 2006 Patrick Hanks