<p><strong>Noun:</strong></p><ul><li>A person or thing occurring singly, especially an individual set apart from others.</li><li>A child or animal that is the only one born at one birth: a research program involving twins and singletons.</li><li>An only child in a family.</li><li>Chiefly British: an unmarried person; a single.</li><li>Cards: a card that is the only one of a suit in a hand.</li><li>Mathematics: a set consisting of one given element.</li></ul>