WordNet sense 1 (troops trained to fight on horseback):

cavalry, horse cavalry

WordNet sense 2 (a framework for holding wood that is being sawed):

sawbuck, sawhorse

WordNet sense 3 (a chessman shaped to resemble the head of a horse; can move two squares horizontally and one vertically (or vice versa)):

knight

WordNet sense 4 (a padded gymnastic apparatus on legs):

gymnastic horse

WordNet sense 5 (solid-hoofed herbivorous quadruped domesticated since prehistoric times):

Equus caballus