WordNet sense 1 (one of four equal parts):

quarter, one-fourth, quartern, fourth part, twenty-five percent

WordNet sense 2 (coming next after the third and just before the fifth in position or time or degree or magnitude):

quaternary

WordNet sense 3 (being or denoting a numerical order in a series):

ordinal

WordNet sense 4 (in the fourth place):

fourthly