More info about the name "Isa"
Isa is a diminutive of Isabella. Isabella is a variant of Isabel. Isabel originates in Latin language and means "promise of God". Ultimately, it is derived from Elizabeth, originating in Hebrew. Some sources suggest that Isabel is simply a Spanish and Portuguese form of Elizabeth. Most recently, the name Isabella was popularized by the character Isabella Swan in Twilight series written by Stephenie Meyer. Currently, it is a number one in the chart of popular feminine given names in the United States.