Short answers, pulled from the story.
The word infantry entered English usage around the 1570s to describe soldiers who marched and fought on foot. This term derives from Middle French infanterie, which traces back to older Italian and Spanish forms meaning foot soldiers too inexperienced for cavalry work.
The root Latin word īnfāns means without speech or newborn, sharing its origin with the modern word infant. Individual soldiers did not receive the specific title infantryman until 1837 when that designation finally appeared in print.
From the mid-18th century through 1881, the British Army named its units as numbered regiments of Foot to distinguish them clearly from cavalry and dragoon regiments. Infantry equipped with special weapons often adopted names based on those tools, such as grenadiers for their grenades or fusiliers for their fusils.
The organization of military forces into regular units first appears in Egyptian records of the Battle of Kadesh. Soldiers grouped into units of 50 which then formed larger units of 250, 1,000, and finally up to 5,000 as largest independent commands.
An infantryman's military kit generally includes combat boots, battledress or combat uniform, camping gear, heavy weather gear, survival gear, secondary weapons, ammunition, weapon service kits, health items, mess kits, rations, filled water canteens, and other consumables needed for operating away from base units. One of the most valuable pieces of gear is the entrenching tool, a folding spade used to dig defenses or perform daily tasks.