If you’ve ever seen anything army related, movie, book, you will know that we call the soldiers that operate on foot, infantry. This component of the army is the biggest, it has the most people in it too. Infantryman as they are called, the words meaning in Latin is non speaking, just like an infant who doesn’t reply back or refute back orders, soldiers were well trained to not answer back at a superior. Infantry also meant army ant in Latin, ants are the only other species than the humans to use army formations.
The word soldier comes from the word Solidus which meant a gold coin because it wasn’t cheap to raise an army of mercenaries.