I would imagine that Mary Poppins didn't call it an umbrella, but the original script could not make it past 1960s era network censors. People exclaiming "Nice bumpershoot!" as she flew overhead probably made them uncomfortable. You really can't blame them, with all those Cockney colloquialisms & such...you never really know what they are saying. ("I've made an error...do you have a rubber?" sounds like the proverbial barn door and horse.)