In the chapter titled "The Bridge of Khazad-Dûm", in The Fellowship of the Ring, Legolas is the first member of the Fellowship to see the Balrog known as "Durin's Bane". He proceeds to alert the others by crying out:
"Ai! Ai! A Balrog! A Balrog is come!"
Whatever it means, "Ai!" is probably one of the least important words in this sentence. Still, I can't find a single canonical translation of the word. Some sources translate it as "Ah!", which doesn't make sense in this context. Others translate it as "Oh!", which makes only slightly more sense. And some translate it as "Hail!", which does make sense in this context (I think we might interpret this as something like "Hey!" in modern English).
Are any of these translations accurate, or does it mean something else entirely? Does it mean anything at all, or is it simply an exclamation with no inherent meaning of any kind (like, for example, "AAAAAAAAAHHHH!")?