Not producing the desired effect; ineffective; failing to accomplish its purpose.
From Latin 'in-' (not) + 'efficax' (powerful, effective), from 'efficere' (to accomplish). A politely devastating word — it doesn't say 'useless,' it says 'not producing desired effects.' Much classier.
When something doesn't work but you want to sound VERY polite about it: 'Your solution was... inefficacious.' It's the fancy way to say 'nice try, but no.' Diplomats LOVE this word! 🎩
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