1. One of four children born at the same time from the same pregnancy
   "The parents were overjoyed to welcome quadruplets into their family";
   - quad
    
2. A set of four similar things considered as a unit
   "The quadruplet of seasons defines the year";
   - quartet, quartette, quadruple

Derived forms: quadruplets

Type of: set, sib, sibling

Encyclopedia: Quadruplet