Dictionary / Vocabulary / 口が軽い
くちがかるい
having a loose tongue; being talkative; speaking without thinking; being unable to keep a secret
Also written 口がかるい
彼女は口が軽い。
She is a chatterbox.
あいつは口が軽いからこのことは言わない方がいい。
Don't tell him. He's got a loose tongue.
彼は口が軽い。
He has a big mouth.