The term 'SOLDIER's Knife' can be summarized as a BAYONET, which is a 7-letter word. A BAYONET is a knife or dagger-like weapon designed to fit on the end of a rifle or musket. It was originally used in close combat during the 17th century, but has since been adapted for use in modern warfare. Bayonets are still used today by military personnel for a variety of purposes, including self-defense and utility tasks.