Also, domesticated horned animals like bulls, rams, and billy goats can often be observed mounting their female counterparts, which could easily contribute to the origin of the word.
Horns have been a prized possession for millennia. They could be used for tools, weapons, ornaments and religious ceremonies. Even today, people buy knives, chandeliers, mantle decorations and centerpieces made from animal horns and antlers.
It was thought, since horns were such powerful possessions, grinding one down into powder and consuming it would make people horny! Even today, the white rhino is hunted for its horn, which sells as a snake oil cure for cancer, hangovers, and as an aphrodisiac!
However, the origin of horny is a bit cruder…
A man’s penis, when erect, sticks up. Centuries ago, this was called, having ‘The Horn.’ Humans don’t have horns of their own. Duh! But because an animal horn was powerful, useful and coveted, of course the erect male appendage was named after it! It was an ego thing! Having ‘The Horn’ was soon shortened to ‘Horny.’
Because only men could have ‘The Horn,’ though anyone could be horny, the term quickly died out as a gendered oriented word. Now, both men and women who are sexually aroused can be described as being horny!
Have fun with that!