Pronunciation: (i-kwes'trē-un),[key] —adj. 1. of or pertaining to horseback riding or horseback riders: equestrian skill. 2. mounted on horseback: equestrian knights. 3. representing a person mounted on a horse: an equestrian statue. 4. pertaining to or composed of knights or mounted warriors: an equestrian code of honor. 5. of or pertaining to the ancient Roman equites.