Meaning

adjective feeling great sexual desire

adjective having horns or hornlike projections

adjective made of horn (or of a substance resembling horn)

originFrom the horn (“an erect penis”) + -y (“having the quality of”). The adjective originally meant "erect", but was later was broadened to refer not only to sexual arousal but also to sexual desire in general.

Etymology from Wiktionary, CC BY-SA 3.0