I am trying to see if the colloquial usage of night and day is non-standard and is improper register, or if it is simply an ommitted definition in the dictionaries:

night and day: Describing a contrast between two completely different things, often one that has resulted in improvement. Often preceded by "like."

The context is from an interview where a person talks about a course where she learned a lot:

I loved the course. Life was totally different. It was just night and day.

This question already covers quite some discussion about the matter: Is the usage of “night and day” as “completely different” very common?

However it does not clarify if this is non-standard or should be avoided. It struck me that none of the standard authoritative dictionaries I checked (about 10 of them) even mention this definition of the idiom, only the "continually" meaning, so I started to wonder if this usage is frowned upon on non-standard.

I have heard it countless times in spoken English, but I would expect it to be in a dictionary at least, mentioning it is spoken as needed. But in addition to the slang/idiom dictionaries mentioned in the linked post, I found it only on The Free Dictionary also in its idiom section only, the definition I pasted above. The definition mentions that it is often preceeded with "like", which is also mentioned in the accepted answer to the linked post.

Does somebody actually know a dictionary definition? Does someone have an explanation why is it not listed as a definition in any of the main dictionaries? And does this missing definition mean that it should not be used in proper speech/writing?

  • There are two different dictionaries which give the dissimile involving 'night and day' at your link. There are three at TheFreeDictionary, again dictionaries of idioms (which, as this is an idiom, one would expect). In fact, the Mcgraw-Hill Dictionary of Idioms ... labels the usage as a cliché: it's overused. Farlex includes the like-less example 'Her transformation has really been night and day.' Commented Jan 26, 2018 at 23:38
  • @EdwinAshworth are you willing to post that as an answer so he can accept it? I'll upvote it ... :o) Commented Jan 26, 2018 at 23:39
  • @Will Crawford I'm not happy with the question. The answer is little less than general reference, and OP has mentioned research but failed to post the above. Idioms can be located in dictionaries of idioms more frequently than in mainstream dictionaries. // The Farlex example I mention above is found by accessing the link in the relevant entry. Commented Jan 26, 2018 at 23:48
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    Mostly fair enough, but the question about whether it's “improper register” at least deserves a resounding No ... Commented Jan 26, 2018 at 23:50
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    It usually takes some time for the major dictionaries to catch up with new usages. This question certainly provides challenges in finding perhaps the single reference that is actually appropriate. But I'd say that the inclusion of 'Her transformation has really been night and day.' without caveat in the Farlex reference means that this usage has become more accepted than inclusion in The Online Slang Dictionary say might imply. Commented Jan 27, 2018 at 0:06

1 Answer 1


By itself, the phrase night and day means "all the time", as shown in ODO

All the time; constantly.
she studied night and day

The "complete different" meaning only arises when you use it in the context of a contrast. Dictionary.com lists this idiom:

a complete difference; completely different:
The improvement in her grades after tutoring was like night and day.

The phrase is usually used after "like", but it's not uncommon to elide noise words like that. It doesn't make it a different phrase, just a variation in use.

There are other similar idioms, such as apples and oranges:

Used with reference to two things that are fundamentally different and therefore not suited to comparison.
unless you also drove a Corolla on the same roads as the A8, you're comparing apples and oranges

In my experience, night and day is usually used to describe a radical change in something (the metaphor refers to the changes that take place in the world when nighttime changes to daytime), while apples and oranges is used to refer two different things or concepts.

  • Great. Does this then simply mean that it is an ommitted definition yet still a standard contemporary usage (as in my context, without the conjunction like)?
    – ib11
    Commented Jan 26, 2018 at 23:19
  • @ib11 Why do you think it's an omitted definition? It's in one dictionary but not the other. I don't have access to OED, but I'll bet it's listed there.
    – Barmar
    Commented Jan 26, 2018 at 23:21
  • Do you think there should be different definitions for "like night and day" and just "night and day"?
    – Barmar
    Commented Jan 26, 2018 at 23:22
  • No, I don't think there should be, but at least one of them (either "night and day" or "like night and day") should appear as a second meaning after "continually", but it does not but in a very few dictionaries, and not in any of the authoritative ones. This is why I posted.
    – ib11
    Commented Jan 27, 2018 at 0:07

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