Thayer's Greek Lexicon

 1. a horn
  1) of animals
  2) since animals (esp. bulls) defend themselves with their horns,
the horn with the Hebrews (and other nations) is a symbol of
strength and courage, and used as such in a variety of phrases
1b1. a mighty and valiant helper, the author of deliverance,
of the Messiah
  3) a projecting extremity in a shape like a horn, a point, apex:
as of an altar