To accouter a soldier is to dress her in military garb and provide her with the equipment she needs. A boy who runs away to join the army might first accouter himself in a camouflage jacket and steel-toed boots.
The verb accouter most commonly describes a soldier being outfitted for battle or a person dressing in some impressive uniform or outfit. You could, for example, say that your friends like to accouter themselves in feathers and sequins before they march in the Mardi Gras parade. The word can also be spelled accoutre, and both versions come from acostrer, "arrange, put on clothing, or sew up," from the Latin roots ad, "to," and consutura, "a sewing together."