The quality of being dextrous; skillfulness and cleverness, especially in handling things with your hands or in tricky situations.
From dextrous + -ness (Old English suffix forming abstract nouns). This noun form solidified in English during the 1600s-1700s as the adjective became established.
The abstract noun form lets us talk about dexterity as a quality—which is why surgeons brag about their 'dextrousness' rather than just saying they're 'dextrous'!
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