口くちを滑すべらせる

expression, ichidan verb

make a slip of the tongue; blurt out; say inadvertently

Used when someone accidentally says something they shouldn't have, often revealing a secret or true feeling.

• つい口くちを滑すべらせて、彼かれの秘ひ密みつを話はなしてしまった。

  I accidentally let his secret slip out.

• お酒さけを飲のんで口くちを滑すべらせる人ひとが多おおい。

  Many people blurt things out when they drink.