noun

• A set of one, an item not part of a larger set, particularly
• (physics) A multiplet having a single member, especially a single spectroscopic peak.
• (physics, quantum mechanics) A quantum state having zero spin.
• (psychology, informal) A person who does not have a form of multiplicity, i.e. a single persona occupying one human body.
• A single piece of clothing, particularly
• (UK, Australia, Ireland, Nigeria, New Zealand, Singapore) A sleeveless buttonless shirt with a low-cut neck.
• (sports) A one-piece, tight-fitting uniform, usually made of spandex or nylon, required in wrestling and powerlifting.