1
- fourth in order or rank; belonging to the fourth order第四的; 第四位的。
2
Quaternary
Geology of, relating to, or denoting the most recent period in the Cenozoic era, following the Tertiary period and comprising the Pleistocene and Holocene epochs【地质】第四纪（岩石）的; 第四系（岩石）的。
3
- Chemistry denoting an ammonium compound containing a cation of the form NR+4, where R represents organic groups or atoms other than hydrogen【化】四元的; 四价的。
3.1
- (of a carbon atom) bonded to four other carbon atoms（碳原子）连上另四个碳原子的。
noun
the Quaternary
- Geology the Quaternary period or the system of deposits laid down during it【地质】第四纪（岩石）; 第四系（岩石）。
The Quaternary began about 1, 640, 000 years ago and is still current. Humans and other mammals evolved into their present forms, and were strongly affected by the ice ages of the Pleistocene.
词源
late Middle English (as a noun denoting a set of four)： from Latin quaternarius, from quaterni 'four at once'， from quater 'four times'， from quattuor 'four'.