There was the following line in December 2nd AP News,

“Chief White House trouble shooter for healthcare gov.web site says the web site is night and day from where it was October 1st. Jeff Zients say they carried out hundreds of software and hardware fixes.

I first took “night and day” for “continually,” but later realized it meant the status of web site is compretely different (mproved) from October 1st stage after searching for the definition of “night and day” other than “all the time,” and found it in Online slang dictionary and urbandictionary:

While all major dictionaries only provide ‘all the time” implication, both Slang Dictionary and Urbandictionary provide “completely different” implication as shown below:

Cambridge Dictionaries Online:

night and day (also day and night) all the time: [ex.] They've worked night and day to publicize their campaign.

Oxford Dictionary:

all the time; constantly: [ex.]She studied night and day

Merriam-Webster Dictionary

all the time: continually

Dictionary com.:

unceasingly; continually: [ex.] She worked night and day until the job was done.

The Online Slang Dictionary:

completely different.


A phrase used to describe a stark difference between two things. Similar to day and night, except it implies an improvement of the situation rather than a deterioration.

So my question: Is the usage of ‘night and day” in the meaning of “completely different” popular, or still on the sideline? Because I don’t find it in any of Cambridge / Oxford / Merriam –Webster English Dictinoary.

  • 4
    "They worked day and night for a whole month, with the result that their website is now night and day different from what it was before." :)
    – F.E.
    Commented Jan 1, 2014 at 0:41
  • Yes it is. They're considered opposites. Commented Jan 1, 2014 at 0:51
  • 2
    I have never, in my lifetime, in Britain heard the expression used in that way i.e. of something being 'night and day different'. Sometimes people, especially politicians, will say 'As sure as day follows night...' e.g. 'As sure as night follows day, higher government expenditure will lead to inflation and the loss of jobs'.
    – WS2
    Commented Jan 1, 2014 at 1:04
  • 4
    The common expression is the dissimile 'as different as night and day'. Looking up the 'completely different' usage, I've not come across many independent examples. The song including this usage may well have popularised it, but it sounds unusual to me. Commented Jan 1, 2014 at 1:06
  • It almost certainly relates to "like black and white", and probably other idioms.
    – Stuart F
    Commented Aug 5, 2023 at 19:37

4 Answers 4


Yes, it is very common. We (US) say, like night and day to indicate opposites. Google "like night and day" and you'll see the option for idiom. completely different:

On snooping disclosures, AT&T and Internet companies are like night and day. -pcworld
Bar Sue and the London Plane Are Like Night and Day: Two Reviews -DC newspaper

Interestingly, "like night and day" gave me hits for many of the dictionaries you listed.

The spokesperson used the idiom abnormally, truncated into an adjective form, instead of as the simile it is.

  • 6
    I'd say "like night and day" is quite commonly used in the UK too. However, without the "like" I'd probably be just as confused as @Yoichi Oishi.
    – tobyink
    Commented Jan 1, 2014 at 10:14
  • 1
    Farlex under "night and day" gives both senses.
    – Stuart F
    Commented May 19, 2023 at 20:13

Night & Day is similarly used to "black and white" therefore opposites. Implying a preference for one or the other and therefore an improvement is not common usage.

  • 1
    But how does this address OP's question Is this usage of 'night and day': 'the web site is night and day from where it was' common?? Commented Jan 1, 2014 at 1:09
  • Welcome to EL&U, synergist. We appreciate your input. This is more of a "comment" than an answer, or may not actually address the OP's concerns, but once you have earned enough reputation, you will be able to make comments, which can include opinions and additional information, such as this. :-) Commented Jan 1, 2014 at 1:41

Working day and night, is literal....possibly an exaggeration, but literal, describing a lot of time working. But when night and day are used in comparison to each other, it is metaphoric and means extreme difference, polar opposites, black and white..etc.


I think the difference is the order of the words (which in the case of most dictionaries (like the ones you mentioned), is listed incorrectly).

When people mean continuously (or at least unusually long hours), I've usually if not always heard / seen them say / write "day and night", which makes sense, that "day" comes first, because "day" is the usual work time, whereas working the "night" also implies overtime). This (albeit little known one) actually gets it right:

(idiomatic) All the time; round the clock; unceasingly.

When people mean opposites (usually also with the latter being the better one), I've usually if not always heard / seen them say / write "night and day", which makes sense that night comes first, because: a) "night" is usually associated with "darkness" and its negative connotation which is usually less preferred to the "day's" relative "brightness" and its positive connotation, b) people usually start out worse and (due to education, training, and/or experience, etc.) become better. This (albeit also little known one and only for "idioms") actually lists the "opposites" definition that the well known ones don't:

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.

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