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")