singleton

UK: /ˈsɪŋg^əltən/ US: /ˈsɪŋgəltən/ ,(sing′gəl tən)

WordReference Random House Learner's Dictionary of American English © 2025

sin•gle•ton /ˈsɪŋgəltən/   n. [countable]

1. a person or thing occurring alone.
2. Games a card that is the only one of a suit in a hand.

WordReference Random House Unabridged Dictionary of American English © 2025

sin•gle•ton  (sing′gəl tən), n. 

1. a person or thing occurring singly, esp. an individual set apart from others:
   a research program involving twins and singletons.
2. Games [Cards.] a card that is the only one of a suit in a hand.
3. Mathematics a set consisting of one given element.

• single + -ton 1875–80

Collins Concise English Dictionary © HarperCollins Publishers::

singleton / ˈsɪŋɡ^əltən/ noun

1. an original holding of one card only in a suit
2. a single object, individual, etc, separated or distinguished from a pair or group
3. a set containing only one member
4. a person who is neither married nor in a relationship

Etymology: 19th Century: from single, on the model of simpleton