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1. The cardinal number that is the sum of three and one
   - four, 4, IV, tetrad, quatern, quaternion, quaternary, quaternity, quartet, foursome, Little Joe
    
2. One of four children born at the same time from the same pregnancy
   - quad
    
3. A set of four similar things considered as a unit
   - quartet, quartette, quadruple

Derived forms: quadruplets

Type of: digit, figure, set, sib, sibling

Encyclopedia: Quadruplet