Vocabulary
口を滑らせる
くちをすべらせる
to make a slip of the tongue; to say something inadvertently; to blurt out without thinking
expression
verb
Example sentences
これは二人（ふたり）の間（あいだ）の秘密（ひみつ）だから、他（た）の人（ひと）には絶対（ぜったい）口（くち）を滑（なめ）らせないでくれるな。
This is a secret just between you and me, so don't let it slip out.