The term "nucleus" comes from the Latin word "nucleus", which means "kernel" or "nut". This is a fitting descriptor because the nucleus is the central and essential part of an atom, just as the kernel is the central and essential part of a nut.

The term was first used in the 1800s to describe the central part of a cell, and later applied to the central part of an atom. This highlights the core role that the nucleus plays in both biological and atomic structures.