There isn't one single perfect synonym for "fungus," as the word itself encompasses a broad category of organisms. However, depending on the context, you could use words like:

General terms:

* Mold: This is often used for fungi that grow on surfaces and cause decay.

* Mushroom: This is a specific type of fungus with a fruiting body.

* Mycete: A more scientific term for a fungus.

* Fungi: The plural form of fungus.

More specific terms:

* Yeast: A single-celled fungus.

* Mildew: A type of fungus that grows on surfaces, often leaving a powdery residue.

* Mycelia: The network of thread-like structures (hyphae) that make up the body of a fungus.

* Spore: A reproductive unit of a fungus.

The best word to use depends on the specific type of fungus you're referring to and the context of your writing.