The word "un-horse" means to remove or throw off from a horse. Antonyms for this word could include words like saddle, mount, ride, or even terms that generally mean riding or being on a horse, such as gallop, canter or horseback. Some other antonyms could be related to the idea of being stable or secure on a horse, such as balanced or supported. Additionally, antonyms could be related to the opposite of being unseated from a horse, such as immobile, stationary, or anchored. Overall, antonyms for "un-horse" carry a sense of stability, security and being firmly in place, which is the opposite of being thrown off a horse.