The quality or state of being acquainted with something or someone; the degree of familiarity or knowledge.
From acquainted (the past participle of acquaint) plus -ness (Old English, meaning 'state or quality'). The -ness suffix is one of the most productive suffixes in English for creating abstract nouns from adjectives.
The word acquaintedness lets us talk about how familiar we are with something—'his acquaintedness with the subject matter was impressive'—it's a formal way to describe degrees of familiarity!
Complete word intelligence in one call. Free tier — 50 lookups/day.