"Zi" means adulthood and respect. "Sum" is summation which is adding a sequence<an ordered list of objects. "Bo" means to live. Zisumbo means a person(or people) that come into your life that makes it better(or in order). This person(or people) builds-up your maturity and respect for others.This person is a "helper".
My friends and family are really zisumbo and that's the reason why I love my life so much.