quaternary in WordNet English dictionary

1. the cardinal number that is the sum of three and one
   four  4  IV  tetrad  quatern  quaternion  quaternary  quaternity  quartet  quadruplet  foursome  Little Joe 
   

1. coming next after the third and just before the fifth in position or time or degree or magnitude
   "the quaternary period of geologic time extends from the end of the tertiary period to the present"
   fourth  4th  quaternary 
   
2. consisting of or especially arranged in sets of four
   "quaternate leaves"; "a quaternary compound"
   quaternate  quaternary