Excellent or wonderful, especially in British English; or the act of breaking something with force.
From the verb 'smash' (break forcefully), but as an adjective meaning 'excellent,' it evolved as British slang in the early 1900s, possibly relating to the idea of something 'striking' or 'outstanding.'
British English speakers embrace 'smashing' to mean excellent while Americans rarely use it that way—it's a perfect example of how the same word can drift to totally different meanings across the Atlantic.
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