In other words = clarify something that has just been said. e.g. There are conference, meeting and banqueting rooms, in other words, the hotel has many facilities.
Mark my words = take note of what I’m saying. e.g. Mark my words, he’ll come back for revenge. He doesn't give up that easily.
My word! = an expression showing surprise, annoyance. e.g. My word! What a mess!
Not a word = Don’t say anything. e.g. I can hear them coming. Not a word or you will ruin the surprise.
Words fail me = to show surprise, shock, happiness, anger e.g. I won the lottery. I can’t believe it. Words fail me.
One more word out of you = punishment will follow if there isn’t silence e.g. One more word out of you and you’ll be sent to your room.
You can take my word for it = believe me e.g. Take my word for it, she’s an excellent teacher.