Jumbo is not used in the US. If you hear the word it is generally someone from a country other than the US.
Back in the '70s, the term Jumbo or Jumbo Jet was indeed used in the USA...
at least in layman's terms.
The reason (this is just a guess) that the 747 is/was referred to as a jumbo was because, at the time, (and still is if one discounts the A380) it was the largest commercial airliner.
If you watch any movies from the 70's and even early '80s that involve airplanes, the term 'jumbo' or 'jumbo jet' is almost always used in reference to the 747.
Widebody is a more broad-ranged term describing ALL
"TransEastern! You'll feel like you've never left the ground because we treat you like dirt!" SNL Parady ad circa 1981