Definition of singlet in English:

singlet

noun

1British A sleeveless garment worn under or instead of a shirt; a vest.
- ‘Equally as beautiful as his womenswear, this featured plain white singlets studded with gold sequins, low-slung cream trousers and kimono print shirts.’
- ‘Winter has settled in, you're not wearing a singlet under your business shirt and you have your first sneeze… she thinks you caught pneumonia and you're going to die.’
- ‘Tommy is wearing a baseball cap, a singlet and combat shorts, revealing several tattoos.’
- ‘Others had on only singlets and cotton trousers as they jumped into the water.’
- ‘Alas, after a while, the sight of board shorts, singlets, jandals and sunglasses will make you wince.’
2Physics
A single unresolvable line in a spectrum, not part of a multiplet.
- ‘Superimposing such a diffractive structure on an aspheric surface yields an achromatic singlet whose spherical and chromatic aberrations are corrected.’
- ‘To break supersymmetry using the F-term, one can add chiral multiplets that transform as singlets under the gauge symmetries in the theory.’
- ‘The singlet is detectable as a quintet at room temperature in methemoglobin with identical spectral features to those of the well characterized tyrosyl radical in photosystem II.’
1. 2.1 A state or energy level with zero spin, giving a single value for a particular quantum number.
  ‘Its superconductivity is often assumed to be unconventional in that the Cooper pairs are not in a spin singlet state with s-wave symmetry, as with conventional superconductors.’
  ‘Do aggregates of A2E have a higher singlet-oxygen quantum yield rather than monomers?’
  ‘The reorganizational energy of the singlet ET was also calculated from the temperature-dependent data and found to be 0.89 eV.’
  ‘A small singlet-triplet energy gap is known to favor intersystem crossing.’
  ‘Energy can be transferred from the singlet state to the triplet state via intersystem crossing.’
3Chemistry
An atomic or molecular state in which all electron spins are paired.
as modifier ‘singlet oxygen’
- ‘The study of the excited states properties has shown that its photoreactivity in neutral aqueous medium is singlet initiated.’
- ‘And where does the singlet oxygen, the energy source, come from?’
- ‘However, reactive oxygen species generated by UVA radiation, particularly singlet oxygen, can also damage nucleic acids.’
- ‘The origin of the initial spike observed upon detection of singlet oxygen luminescence remains unresolved.’
- ‘It can thus be regarded as a simultaneous excitation of two triplets, whose coupling generates an overall singlet state.’