So they take a word "whitespace" which needs no hyphen and jam one in. Then they take two completely distinct words "no wrap" and jam them together with no separator. And then you have to remember both of these on the same rule.
Also, the entire semantics are a bit strange. When I'm deciding whether I want text to line wrap, I don't really think about whether the whitespace should wrap. Yes, whitespace is somewhat relevant to the topic, since that's one option of where to break lines in order to line wrap, but I still think of it as the entire text that is line wrapping.
Oh, and don't forget that there is in fact a word-wrap property, which is a much better name for the previous behavior, but in fact only customizes how the line-breaking algorithm determines which words can be broken apart.
The naming is far from great, but there is a method to the madness. Here's a talk I did a while back on how various line breaking things fit together: https://cssday.nl/2019/speakers#florian
This is at the top of the list in the Incomplete List of Mistakes in the Design of CSS[1]. Which has been discussed several times on HN (last 2 months ago)[2].
As far as I can tell, both are common, but “white space” is more common as a synonym to negative space, and “whitespace” is more common to refer to the characters. If so, the “white-space” property controls whitespace, not white space.
