The quality or state of being egregious; extreme badness or shockingness that stands out obviously.
From 'egregious' plus the noun-forming suffix -ness, which derives from Old English and Germanic roots meaning 'condition or quality of.'
English loves stacking suffixes—egregious → egregiously → egregiousness shows how one Latin root can grow into a whole family tree of related words expressing the same idea with different grammatical flavors.
Complete word intelligence in one call. Free tier — 50 lookups/day.