Clarify description in NEWS.md

Author: cmcaine

NEWS.md

@@ -94,7 +94,7 @@ New library functions
 * New function `insorted` for determining whether an element is in a sorted collection or not ([#37490]).
 * New function `Base.rest` for taking the rest of a collection, starting from a specific
   iteration state, in a generic way ([#37410]).
-* New function `isgreater(a, b)` defines a descending total order where unorderable values and missing are ordered smaller than any regular value.
+* New function `isgreater(a, b)` defines a descending total order where `missing` and normally unordered values, such as `NaN`, are ordered smaller than any regular value.
 * Two argument methods `findmax(f, domain)`, `argmax(f, domain)` and the corresponding `min` versions ([#27613]).
 
 New library features