noun
infantry
IN-fun-tree/ˈɪnfəntri/
Soldiers trained and equipped to fight on foot.
The infantry marches across the training field carrying packs.
Etymology
French infanterie named foot soldiers collectively. Behind it was a word meaning 'youth,' applied to soldiers considered too inexperienced or low in rank for cavalry, linking childhood vocabulary with troops who fought on foot.
In context
fought on foot and were armed differently than knights this leads us back to the core argument of the infantry revolution it's not that cavalry became useless but that infantry gained in importance