The Etymologies state that h- is prefixed to the word following this preposition, when it begins with a vowel: o Hedhil "concerning the Elves". Some scholars consider that this rule is not valid in Sindarin, but that the preposition would perhaps become oh in such a case (hence oh Edhil, to be compared with ah in Athrabeth Finrod ah Andreth)
The Etymologies state that h- is prefixed to the word following this preposition, when it begins with a vowel: o Hedhil "concerning the Elves". Some scholars consider that this rule is not valid in Sindarin, but that the preposition would perhaps become oh in such a case (hence oh Edhil, to be compared with ah in Athrabeth Finrod ah Andreth)