Other forms: musketeers
In the old days, a musketeer was a soldier who was armed with a muzzle-loading long gun.
Before World War I, a musketeer was a member of the infantry who carried a specific type of weapon called a musket. Today, you're probably most likely to find this word referring to the famous novel by Alexandre Dumas called "The Three Musketeers." If you guessed the book is about three soldiers who carry muskets, you're right! It's also not unusual for adults to describe a group of three close pals as "the three musketeers."