WordNet sense 1 (a land mass that projects well above its surroundings; higher than a hill):

mountain

WordNet sense 2 (a mounting consisting of a piece of metal (as in a ring or other jewelry) that holds a gem in place):

setting

WordNet sense 3 (something forming a back that is added for strengthening):

backing

WordNet sense 4 (a lightweight horse kept for riding only):

saddle horse, riding horse

WordNet sense 5 (get on the back of):

bestride, get on, hop on, climb on, jump on, mount up

WordNet sense 6 (go upward with gradual or continuous progress):

climb, go up, climb up

WordNet sense 7 (prepare and supply with the necessary equipment for execution or performance):

put on

WordNet sense 8 (copulate with):

ride

WordNet sense 9 (go up or advance):

rise, wax