I've never heard anyone call it anything other than dish/dishing. Most tool makers (Park, EVT, Abbey, etc) calls the tool a dishing tool, (Some call it a wheel alignment gauge) and every wheel builder I've spoken to says to "check dish".

I have heard it used both as a noun and as a verb. I looked at photos from my wheelbuilding class and the instructor wrote on the whiteboard: "Dish to < 0.2mm gap".

Calvin Jones and Ric Hjertberg use the term dish, as does Saint Sheldon (he uses the term "dish stick" for the tool). Jobst Brant uses the term dish, but calls the tool a "Centering Bridge".

I am curious what pro mechanics do call it - I guess I don't know any pros, only people who work in bike shops or those who build wheels for a living.