Definition of "subbing"

With the best will in the world, excluding any assumption that the Berlin paper would wish to make Einstein look ridiculous, or that the Times man overemphasized any anti Americanism, these choppings, subbings, and translations inevitably did more than alter the balance of the original.

1971, Ronald Clark, Einstein: The Life and Times

Do not expect to sub (or copy edit, as the Americans call it) your article to perfection in one go - I will do three or four subbings before I'm convinced an article is as perfect as I can get it. But when you've done all you can - yes, send it out!

2007, Diana Cambridge, How to Write for Magazines...in One Weekend, page 69