There's no separate word for the masculine form of "male deer" because it's already specifying the gender.
However, depending on the species of deer, you could use more specific terms like:
* Buck: This is the most common term for an adult male deer.
* Stag: This term is often used for red deer, but can also be used for other species.
* Hart: This term is used for male fallow deer.
* Billy: This term is used for male goats.
The term you use will depend on the context and the specific species of deer you're referring to.