An Etymological Dictionary of Astronomy and Astrophysics

The last two million years of geologic time, comprising the Pleistocene and Holocene glacial epochs. Estimates of the date of the beginning of the Quaternary vary between 2.5 and 1.6 million years ago.

Etymology (EN): Quaternary, from L. quaternarius “consisting of four,” from quatern(i) “fourt at a time” + -arius “-ary;” → period.

Etymology (PE): Dowrân, → period; cahârom “fourth,” from cahâr “four” + -om “-th.”