1. singleton(n = noun.quantity) - a single object (as distinguished from a pair);
is a kind of 1, ace, i, one, single, unity
has particulars: fellow, mate
2. singleton(n = noun.group) - a set containing a single member;
is a kind of set
3. singleton(n = noun.artifact) - the playing card that is the only card in a suit held in a bridge hand as initially dealt;
is a kind of playing card
In certain games at cards, as whist, a single card of any suit held at the deal by a player; as, to lead a singleton. [1913 Webster]
singleton, n.
1 one card only of a suit, esp. as dealt to a player.
2 a a single person or thing. b an only child.
3 a single child or animal born, not a twin etc.
Etymology:
SINGLE, after simpleton