Is there a word that can be used to describe a group or collection that only has 1 member/element? I first thought of singleton, but in my context singleton has a well-established meaning and I want to avoid confusion.

I want to ask a question like, "Does the group contain only one member?" with a more succinct, "Is the group a <insert-word-here>?" An analogous one would be: to ask if the group contains no elements, "Is the group empty?"

Put another way: empty is to "group with 0 elements" as <?> is to "group with 1 element."

"Bonus points" for a word that helps answer this more specific question succinctly: "Does the group contain only this one specific member?"

Clarification: The "group" can have different number of elements at different times. Subsequently, in that context a "group" ("collection" if you prefer that word.; eg, a Set, List, Array, etc) can contain 0 or more elements and still be a valid "group")

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    Reminder: comments are to ask for clarification. If your comment has been removed here, it's because it didn't contribute to that.
    – Andrew Leach
    Jul 27, 2018 at 8:55
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    Can you clarify what sort of "group" you are thinking of? Group of people? Collection/list of items in a computer data structure? Or ...
    – user184130
    Jul 27, 2018 at 14:24
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    Would a more succinct way to say "an individual that is the only member of its kind" work for you? "Group of 1" is harder, since groups, by definition, usually consist of more than one member. If it really needs to be a term for a group, do you want a term that means "a group that can only fit one member" or instead "a group that only currently contains one member, but there's room for more"?
    – 1006a
    Jul 27, 2018 at 16:46
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    I'm voting to close this question as off-topic because the question is asking for some type of technial word. And See also the closed Can you call two things a “group”? Jul 27, 2018 at 19:18
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    I just reverted the title. @user please do not change it again, you are altering the intent and spirit of my original question and that's not friendly SE behavior.
    – E-Riz
    Jul 27, 2018 at 21:23

4 Answers 4


Although 'unary', that is,

3. Composed of a single item or element.

OED Online

(alternatively defined here and here) is an adjective, it suits your desire for succinctness if the article is omitted: "Is the group unary?"

  • Your OED link doesn't seem to work. Maybe this: en.oxforddictionaries.com/definition/unary
    – user184130
    Jul 27, 2018 at 19:06
  • @JamesRandom, thanks, but that is not where the definition came from. The quote is correctly attributed and the link works (for me; the definition is possibly behind a paywall for you).
    – JEL
    Jul 27, 2018 at 19:08
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    Nope, the link isn't useful.; it just points to the home page of the OED website. I don't think SE answers should point to sites you have to subscribe to and pay for as references. My opinion.
    – E-Riz
    Jul 27, 2018 at 21:30
  • @E-Riz, precisely. That, OED Online, is where the quote came from. The link would be broken if it pointed to the definition...unless you have a login and are logged in. "Isn't useful" is not "broken", and my opinion differs. The use is attribution, not access.
    – JEL
    Jul 27, 2018 at 21:34
  • See my edited comment that crossed yours mid-fight. I edited the answer with two additional links that anyone can view. If my edits are approved (or you edit it yourself) I'll accept the answer.
    – E-Riz
    Jul 27, 2018 at 21:38

Singleton is used in computer programming (eg a class that can only have one instance) and in mathematics. For example, for a set containing only one element:

In mathematics, a singleton, also known as a unit set,1 is a set with exactly one element. For example, the set {0} is a singleton.

The term is also used for a 1-tuple (a sequence with one member).


If the word singleton is unacceptable then maybe unit set, 1-tuple or unitary might be better. These all have their own existing meanings in computing and/or mathematics so might also cause confusion.

  • The OP explicitly wants to avoid using singleton Jul 27, 2018 at 13:34
  • Thanks. Edited the answer to make the options more explicit (and add another one).
    – user184130
    Jul 27, 2018 at 14:23

In American accounting, a type of business arrangement is the Limited Liability Company (LLC). An LLC can have several members or a single member. The Internal Revenue Service classifies an LLC with a lone member as a single-member LLC.


The succinct question could be phrased as "Is the the group an individual?", but that isn't exactly an answer for the broader question, since individual doesn't usually imply a group.

The usual phrasing (rather than being a single word) is "committee of one"

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