like night and day
Completely different; totally or nearly opposite. Her transformation has really been like night and day. She doesn't even look like the same person since she started the program. A: "Have you seen any improvement in his behavior?" B: "Oh, it's like night and day. He's been a model student this month."
like night and day
If two things are like night and day, they are completely different. `Compare him with last year and it's like night and day,' his teammate said. Note: People also sometimes just say that two things are night and day. The two stories are night and day.