[ kwə'tə:n(ə)ri ]
■ adjective
1》 fourth in order or rank.
2》 ( Quaternary ) Geology relating to or denoting the most recent period in the Cenozoic era, following the Tertiary period (comprising the Pleistocene and Holocene epochs and beginning 1.64 million years ago).
3》 Chemistry denoting an ammonium compound containing a cation of the form NR 4 + , where R represents organic groups.
Origin
ME: from L. quaternarius , from quaterni 'four at once', from quater 'four times', from quattuor 'four'.