(I) won't (say) anything no matter what (expression is followed by negative verb relating to say, answer, etc.) to not (tell) even under any threatsee also 口が裂けても言えない【くちがさけてもいえない】
(I) won't (say) anything no matter what (expression is followed by negative verb relating to say, answer, etc.) to not (tell) even under any threatsee also 口が裂けても言えない【くちがさけてもいえない】
Lingaku