I’ll definitely say that the term “improper list” has been overloaded to mean many things over the years, and is pretty much now just a catch-all to mean “not a proper list”, which - when read by a newbie - would imply “a list, just not one that is ‘proper’”, given some definition of “proper” (e.g. not circular and ends with nil). But, “not a proper list” does also mean atoms, as @dvanhorn wisely stated. :slightly_smiling_face:

rephrased: add this to the list of pain points that would disappear if cons required its second argument to be a list