1) horses (A passion or obsession with horses[1] as well as a madness in horses[2]) => [hippo-] (Greek) meaning 'horse' [see hippophobia (opposite)] 2) hippopotamuses (passion or obsession with hippopotamuses [3] => [hippo-] (Greek) meaning 'horse' & [ potamos ] (Greek) meaning 'river'.
obsession with horses
hippomania An obsessive fascination for or an excessive enthusiasm for horses.