be out like a light

1. To be sleeping very soundly. Don't worry, the vacuum won't wake him—he's out like a light. The dog's still out like a light. Guess we really tired him out on that long hike this morning! I guess I was out like a light because I didn't hear my alarm for a while. And that's why I'm late to work.

2. To fall asleep quickly. I didn't even hear you come in last night—I was so tired that I was out like a light as soon as my head hit the pillow. A: "OK, I put the baby down, and she's out like a light." B: "Wow, you must have the magic touch!" I'm an insomniac and my husband is always out like a light—it's so annoying.

3. slang To be very drunk. Do you remember last night at the bar at all? You were out like a light! On his 21st birthday, Mike's friends gave him so much to drink that he was out like a light by 10 PM. If I got up and did karaoke last night, I must have been out like a light. How much did I have to drink?

be/go out like a ˈlight

(informal) fall asleep very quickly or suddenly lose consciousness: She went out like a light after an exhausting day at work. ♢ One minute she was talking and laughing and the next minute she was out like a light. It was very frightening.