What was infantry referred to by in antiquity/ancient times?
I did a bit of searching around and found that the term "infantry" didn't start getting used to describe foot soldiers until the 1500's and, individually wasn't officially widely used until the British did so in the 1800's. So from this I gather the term "Infantrymen" is a modern term.
Being based off the Latin word "infans" or referring to ones youth, foolishness or stupidity some would argue that's the reason for using the word to describe the most laborious, simple, and violent military position.
Another possibility is that ancient armies were structured according to family wealth and seniority. Richer, aristocratic men could afford the best armor and weapons, while the younger, poorer, men would be limited in the equipment and thus used as the component to bear the brunt of the fighting.
So why would later civilizations come to use this word to call their most crucial soldiers? It seems a little counter intuitive to me. Maybe they knew that the general public wouldn't have a clue as to what "infantry" actually meant?
And back to my original question, what were foot soldiers called during their respective times throughout history?
Any insights would be helpful.