1. A double number is two identical numbers, e.g. 007 (double O seven)
  2. A double chin is someone who appears to have two chins
  3. A double feature is a program showing two feature-length movies
  4. A double D is a bra with two DD cups
  5. A double standard is a rule or principle which is unfairly applied in different ways to different people or groups (EOD)
  6. A double yolk is an egg with two yolks

All the nouns listed above are countable but stay singular. On the other hand, if we substituted the word double with two the noun is pluralized e.g.

I cracked open an egg and found two yolks

Why don't we use the plural noun in these cases?

  • I cracked open an egg and found double yolks (NO)
  • I cracked open an egg and found a double yolk (YES)

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There appears to be an exception to the rule and it is double doors. According to Ngram, today the plural form compared to its singular counterpart is used 80 times more frequently.
(Hopefully, I didn't mess up the maths, but if I did please correct me)

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3 Answers 3


According to Collins dictionary, double as defined in definition 2:

Adj. You use double before a singular noun to refer to two things of the same type that occur together, or that are connected in some way.

E.g ...an extremely nasty double murder.


Because the subject of is in your examples is the name for something. That thing is understood as a single compound entity or thing.

I bought tickets for the double-header but it got rained out.

  • But the double yolks are inside the egg (?!) And in the sentences the subject is "I" and "a double yolk" is the object.
    – Mari-Lou A
    Nov 12, 2018 at 16:34
  • I am talking about your list of sentences at the top. We don't say She are a triple threat. The reference is to a monad of three. She is a triple threat. A triple threat is what she is.
    – TimR
    Nov 12, 2018 at 17:47
  • +1 for "monad" I had to look it up, I haven't seen that word in years
    – Mari-Lou A
    Nov 12, 2018 at 18:21
  • Monads are crepuscular. But you've probably seen plenty of dyads and triads, tetrads and pentads in broad daylight.
    – TimR
    Nov 12, 2018 at 18:33

"Double" is an adjective describing the noun. The noun determines whether it is singular or plural.

From your examples:

  • double zero or double D- singular
  • double chin - singular
  • double feature - singular
  • double standard singular
  • double doors - plural

"Double-yolk" is a bit of a special case, and is complicated. It's an adjective describing an egg (a "double-yolk egg"), which doesn't actually say the noun. Think of the sentence, "The best of us are happy." you can see that "best" is not normally a plural noun; so where does that "are" come from? "Best" is an ellipsis of the noun phrase, which just means that the actual noun is left out. You can read that as "The best [people] of us are happy," and it will make more sense (or any other noun that matches "us"). In the same way, read "double-yolk" as "double-yolk [egg]", and it will make more sense.

It may be worth noting that many of these also work fine as plural, but have a slightly different meaning:

  • You might have a "double chin" which means your face is shaped a certain way. If so, your "double chins" are the actual face bumps.
  • "Double D" means "DD", most commonly understood as a bra size. "Double D's" are the objects that fit inside such a bra.
  • "Double door" tends to indicate the portal size, while "double doors" refers to the actual swinging piece.
  • Where I come from, a 'double chin' is usually a sign of obesity, rather than heredity. Aug 26, 2022 at 12:49
  • @MichaelHarvey yes? I’m not sure where I implied otherwise.
    – fectin
    Aug 26, 2022 at 12:56

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