Cenozoic

This term is a technical geological designation used primarily in scientific and academic contexts. It carries a neutral, descriptive tone and is almost always capitalized when used as a noun to refer to the specific era, though it may appear in lowercase when used as a general adjective in some scientific styles.

As a noun, the word refers to a unique, singular span of geological time. Because it denotes a specific, one-of-a-kind era in Earth's history, it is treated as an uncountable proper noun and does not have a plural form.