means The quality of being receptive to new ideas, experiences, and people — and willing to share or reveal freely rather than guard and conceal.

from Built from the Old English 'open,' which traces back to Proto-Germanic roots tied to the idea of being 'up' or 'raised' — think of a lid lifted, a door swung wide. The '-ness' suffix is the ancient English machine for turning a quality into a thing: open becomes openness, the state of being open. The psychological sense — one of the famous 'Big Five' personality traits — is a modern academic borrowing of this very old, very physical word.