The quality or state of being broad; wide physical extent or scope of understanding.
From 'broad' + '-ness,' the standard English suffix creating abstract nouns from adjectives (Old English -nes). This allows 'broadness' to describe both physical width and metaphorical openness of mind.
Abstract nouns ending in '-ness' (sadness, brightness, broadness) are one of English's most productive patterns—you can almost add '-ness' to any adjective and create a new word, which is why English absorbs new ideas so easily.
Complete word intelligence in one call. Free tier — 50 lookups/day.