(n): a unit of geological time during which a system of rocks formed
(n): the cardinal number that is the sum of three and one
(n): one of the elements that collectively form a system of numeration
(adj): consisting of or especially arranged in sets of four
(adj): vs. single) -- (having or involving or consisting of more than one part or entity or individual
(adj): coming next after the third and just before the fifth in position or time or degree or magnitude
(adj): vs. cardinal) -- (being or denoting a numerical order in a series
