Princeton's WordNet

1. quadruplet, quad(noun)

   one of four children born at the same time from the same pregnancy

   Synonyms:
   quadriceps femoris, quaternary, quadruplet, quartet, quadruple, quadrangle, quatern, quad, four, quartette, quaternion, quadriceps, space, quaternity, foursome, tetrad, musculus quadriceps femoris

2. quadriceps, quadriceps femoris, musculus quadriceps femoris, quad(noun)

   a muscle of the thigh that extends the leg

   Synonyms:
   space, quadrangle, quad, quadriceps femoris, quadriceps, quadruplet, musculus quadriceps femoris

3. quad, space(noun)

   (printing) a block of type without a raised letter; used for spacing between words or sentences

   Synonyms:
   blank space, outer space, infinite, distance, quad, space, quadriceps, place, quadruplet, blank, quadrangle, musculus quadriceps femoris, quadriceps femoris

4. quad, quadrangle(noun)

   a rectangular area surrounded on all sides by buildings

   Synonyms:
   quad, tetragon, space, quadriceps, quadrilateral, quadruplet, quadrangle, musculus quadriceps femoris, quadriceps femoris