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

• prog
• progenitor
• progeny
• progeria
• progestational
• progesterone
• progestin
• progestogen
• prognathic
• prognathism
• prognathous
• Progne
• Progne subis
• prognosis
• prognostic
• prognosticate
• prognostication
• prognosticative
• prognosticator
• program
• program development cycle
• program library
• program line
• program music
• program trading