HADAD

I would like to know what's mean the surname HADAD, I was reading about It and I found is not a arabic word but is very common in SYRIA and LEBANON , and is a biblic name anyone can find it in GENESIS IN A ESAU'S desendants, therefore is a surname fron EDOMOR IDUMEA, I need to know if somebody know about IT, and what's the difference with HADDAD.