I am no expert, but Nominate may not be the root form of Denominate. Nominate definition > specify (something) formally, typically the date or place for an event Denominate definition > call, name To be denominational is thus to "name" your sect. This name defines a set of believes or particular perspectives held by the sect, regarding the overarching religion. Being non-denominational is to "not call, not name". In essence, to not declare the name of the sect.