Other forms: hornier; horniest; hornily
Things that are horny either look like or are made of an animal’s horn or a similar hard material. The thick, hard nail on your big toe could be described as horny.
The word horny, describing the bony projection on an animal's head, appeared in English before the 10th century. An informal meaning — that of being sexually aroused — appeared later. Male physical arousal was crudely referred to as "having the horn” in the late 18th century before becoming the word horny in the mid-19th century. First used exclusively for men, the word now describes women's sexual feelings as well.