horny

adjective
1. feeling great sexual desire; "feeling horny" [syn: aroused]
2. having horns or hornlike projections; "horny coral"; "horny (or horned) frog"
3. made of horn (or of a substance resembling horn) [syn: corneous]

"lustful, sexually aroused," definitely in use 1889, perhaps attested as early as 1863; from late 18c. slang expression to have the horn, suggestive of male sexual excitement (but eventually applied to women as well)

I'm feeling horny...