I realized most python related terms usually don't have a very serious origin. I remember when I learned that the name for Python's packaging format ("wheels") is short for "cheese wheels"... because PyPi used to be called "The Cheese Shop"!
I always thought it was some sort of reference to the structure of the package or something lol. I like it though!
According to Wikipedia, the term dates back to at least 2002:
> The frequent use of a double underscores in internal identifiers in Python gave rise to the abbreviation dunder; this was coined by Mark Jackson[3] and independently by Tim Hochberg,[4] within minutes of each other, both in reply to the same question in 2002.[5][6]
Knowing that made hem less scary