Explanation

• Equestrian refers to a person who rides a horse, especially as a sport or recreation. It can also refer to something related to horse riding or horses in general.
• Egoist: This word refers to a person who is excessively self-interested or egotistical, and has no relation to horse riding.
• Germicide: This word refers to a substance that kills germs or microorganisms, and has no relation to horse riding.
• Impassable: This word means unable to be passed or traversed, and has no relation to horse riding.