I am looking for a word that describes a set of numeric values divided into three equal, ordered parts. For example, "quartile" refers to subsets of a set that has been divided into four equally-size parts sorted in order (i.e., the first quartile is the set of the first 25% of lowest values, the second contains the next-higher subset of 25% of the values, etc.). Likewise, "quintile" refers to subsets of a set divided into five equally-size ordered parts. "Thirds" is not exactly what I am looking for since dividing something into thirds does not necessarily connote an ordering of items in the set.

Thanks in advance!

I am looking for a word that describes a set of numeric values divided into three equal, ordered parts. 

For example, "quartile" refers to subsets of a set that has been divided into four equally-size parts sorted in order (i.e., the first quartile is the set of the first 25% of lowest values, the second contains the next-higher subset of 25% of the values, etc.). Likewise, "quintile" refers to subsets of a set divided into five equally-size ordered parts. 

"Thirds" is not exactly what I am looking for since dividing something into thirds does not necessarily connote an ordering of items in the set.