From Tolkien Gateway
acas (pl. axi) is a Quenya word meaning "(back) neck" and "rock ridge".
- axë - later form replacing acas.
- ↑ J.R.R. Tolkien, "Words, Phrases and Passages in Various Tongues in The Lord of the Rings", in Parma Eldalamberon XVII (edited by Christopher Gilson), p. 92