Definitions:

1. In childbirth, refers to one of four children born to the same mother during a single pregnancy. NOUN
   • The couple was overjoyed when they learned they were expecting quadruplets, four babies all at once.
2. In general usage, can refer to any group or set of four similar or related items. NOUN
   • The puzzle came in a quadruplet of pieces that needed to be assembled together.
3. In music, is a group of four notes that are played in the time typically allotted for three notes, or occasionally in place of other standard rhythmic groupings, that can alter the rhythm by fitting four notes into a beat or segement where fewer notes are expected. NOUN
   • The composer used a quadruplet in the rhythm to add complexity to the melody.

Synonyms:

• four
• quad
• quadruple
• quartet
• quatern