If people's first impression of what you want your UI to mean is different often enough to cause problems (for example see the amount of debate here), that is the bug, not the people misinterpreting it. The use of these terms in Jira is one of my pet peeves, since different teams often use them very differently and can be real fun when sharing Jira boards with multiple opinionated companies.

The colloquial usage of 'severity' and 'priority' just has too much overlap. Something like pairing 'likelihood' and 'severity' assessments, as is standard in safety, would still be general and make it immediately clear why something could be severe yet low priority, especially since people commonly mean both likely and severe when ranking a problem as severe. Keeping with the author's definition of severe, renaming severity as 'System Impact' at least immediately narrows down what is severe, but still carries the possible implication of 'frequent'.

I think fighting for a given interpretation here without using different terms is akin to insisting that people simply understand that a 'significant difference' reported in science means 'statistically different' as opposed to an 'important difference'.