The quality or state of being galling; the characteristic of being deeply annoying or frustrating.
From 'galling' (adjective) plus the noun-forming suffix '-ness', a common Old English pattern that creates abstract nouns from adjectives to express qualities or states.
The '-ness' suffix is one of English's oldest and most productive word-building tools—you can add it to almost any adjective, which is why we can talk about the abstract 'gallingness' of a bad situation rather than just calling it 'galling'.
Complete word intelligence in one call. Free tier — 50 lookups/day.