Singlet may refer to: singlet state, in theoretical physics, a quantum state with zero spin Singlet fission, in molecular photophysics in spectroscopy, an entity appearing as a single peak; see NMR spectroscopy in optics, a single lens element, the building blocks of lens systems; see lens (optics) a one-piece collarless garment, also known as a sleeveless shirt or vest wrestling singlet, a one-piece garment specific to wrestling BID/60, a British encryption machine Singlet oxygen, the common name used for an excited form of molecular oxygen