What is an adult male sheep called?

An adult male sheep is called a ram.

Rams are male members of the domestic sheep species, Ovis aries. In many breeds, they are distinguished by their heavier build and, sometimes, by prominent horns. Horns are not universal, however: some breeds are naturally polled, meaning they lack horns.

Rams are kept primarily for breeding. Their mating season is often called the rut, and their seasonal reproductive behavior can influence when lambs are born. Farmers select rams for traits such as growth, wool quality, health, and resistance to disease.

A female sheep is an ewe, while a young sheep is a lamb. “Buck” is normally used for a male goat, and “boar” for a male pig, so those terms should not be substituted for ram.