It's not just a semantic difference, it's normally a chemical one, and even in the US, very much a legal one:
https://en.wikipedia.org/wiki/MargarineThe EU has very strict definitions of this, and in the UK (for health reasons I expect), there is no market appetite for a spread that contains partially hydrogenated oils.
In the US, regulations are much more lax and substances that are considered unfit for mass market consumption in Europe (typically for health concerns), such as trans fats, are widely available in the US.
You can dress this up as a "stigma" or a "euphemism", but I call it reasonable consumer protection law.