The quality or state of being demonstrable; the capacity to be shown or proved.
From demonstrable + -ness (a suffix forming nouns indicating a state or quality). This creates a noun form from the adjective demonstrable, similar to kindness from kind.
English lets you stack suffixes endlessly—demonstrable → demonstrableness is like Russian nesting dolls of meaning—but we usually just say 'demonstrability' instead, showing that sometimes languages create multiple words and then pick their favorite.
Complete word intelligence in one call. Free tier — 50 lookups/day.