Hello again Latishya.
link

"For example, classical Latin equus was replaced in common parlance by vulgar Latin caballus, derived from Gaulish caballos (Delamare 2003 p.96), giving Modern French cheval, Catalan cavall, Occitan caval (chaval), Italian cavallo, Portuguese cavalo, Spanish caballo, Romanian cal, and (borrowed from Anglo-Norman) English cavalry and chivalry." (From the article)

Here is equus again. From the article it seems like Old French was more like vulgar Latin? It looks a bit like Esperanto. Is there any literature or well known document left written in Old French?