Superlative form of 'dashy'; the most stylish, lively, or impressively energetic in appearance or manner.
From 'dash' + -y + -est (superlative marker). Follows the standard English pattern for creating the strongest form of adjectives.
The superlative 'dashiest' shows up in historical novels and 19th-century texts describing characters with particular flair, but it's a perfect example of how English speakers constantly create new adjectives on the fly using productive suffixes, and some stick around while others fade away.
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