Possibly an Anglicization of the Welsh name Elisedd, meaning “kind” – and the “son” suffix indicates, you guessed it, the offspring of Ellis. So this name essentially means “child of a kind person,” and unless you’re a total asshole, a fitting choice.
Famous people named Ellison:
TV journalist Ellison Barber; architect Ellison Harvie; astronaut Ellison Onizuka; marathon runner Ellison Myers Brown.
This name may also originate from the Greek name Elias, from the Hebrew Elijah, meaning "the Lord is God."