無効

むこう · mukou · JLPT N1 · na-adj

invalid

無 (mu) = none, 効 = effect: none + effect = no effect, so invalid or unavailable

The same 無 appears in 無料 (no charge, free) and 無理 (not possible). Where 効 is used alone, it means effect or efficacy, as in 効果.

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