When it comes to synonyms for "riding horse," there are several options. One common synonym is "equine," which refers to any animal in the horse family, including horses, ponies, and donkeys. Another option is "mount," which can refer to either the act of riding or the animal itself. "Steed" is a more archaic synonym that carries connotations of a well-bred or noble horse. "Nag" or "hack" are often used derogatorily to refer to a less impressive or unremarkable riding horse. Finally, "charger" is a synonym that emphasizes the horse's role in battle or jousting tournaments. All of these synonyms can be used to add variety and nuance to a description of a riding horse.