The 'origin' of this custom/tradition is not known. = The 'origins' of this custom/tradition are not known. [=no one knows how this custom/tradition started]
He comes from 'humble origins'. [=he comes from a family that did not have high social status or much money]
The English word “rendezvous” is French 'in origin'. [=the English word comes from French]
(..) And the study of clocks is a hobby? This is an obsession. Really my specialty. My practice centres around antiquities. But the origin of this clock completely eludes me. I've never seen anything quite so beautiful that I know so little about. This is a pleasurable torment. My ignorance amuses me. (..)2001 Lara Croft: Tomb Raider