What is another word for bacterium?

There isn't a single perfect synonym for "bacterium," as it depends on the context and the specific type of bacteria you're referring to. However, some common alternatives include:

General terms:

* Microbe: A general term for any microscopic organism, including bacteria, viruses, fungi, and protozoa.

* Germ: This term is often used to describe any microorganism that causes disease.

* Bug: This is an informal term for bacteria, often used in casual conversation.

Specific types:

* Baci (plural of bacillus): This refers to a specific type of rod-shaped bacteria.

* Cocci: This refers to spherical bacteria.

* Spirilla: This refers to spiral-shaped bacteria.

Scientific terms:

* Prokaryote: This term describes a single-celled organism that lacks a nucleus and other membrane-bound organelles. While not strictly synonymous, it encompasses all bacteria.

The best alternative will depend on the specific context of your writing.