triplet
noun /ˈtrɪplət/
  /ˈtrɪplət/
 - one of three children born at the same time to the same motherTopics Family and relationshipsc2
 - (music) a group of three equal notes to be played or sung in the time usually taken to play or sing two of the same kind
 
Word Originmid 17th cent.: from triple, on the pattern of doublet.