Denshi Jisho — Online Japanese dictionary

効果 こうか effect; effectiveness; efficacy; result
Common word, Noun, No-adjective 
効果的 こうかてき effective; successful
Common word, Na-adjective 
効果音 こうかおん sound effect; sound effects
Noun 
効果覿面 こうかてきめん bring an immediate result on; have an instant effect on
Noun 
効果抜群 こうかばつぐん exceptionally effective; overwhelming effectiveness
Noun, Na-adjective, No-adjective 
効果が上がる こうかがあがる to bear fruit; to take effect
Expression, Godan verb with ru ending 
効果の法則 こうかのほうそく law of effect
Noun 

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