A person who is skilled at shooting a gun.
A shootist is someone who is very good at using a gun. It can make people think of cowboys or action movies.
Examples:
The shootist hit the target every time.
The shootist won the shooting competition.
The shootist is the best in the west.
The shootist never misses, not even once!
The shootist can shoot the wings off a fly.
The shootist became famous for his amazing shooting skills.