harry potter - How did Avada Kedavra get its name?

How did Avada Kedavra, the Unforgivable Killing Curse, get its name? Most spells' incantations sound similar to their effect, with their names influenced from Latin.

However, Avada Kedavra, influenced by 'Abra Cadabra', sounds more like a silly phrase a magician in a kids' birthday party would say before pulling a rabbit out of a top hat, not much like a wizard about to commit murder.

Also, unlike the rest, influenced by Latin, Abra Cadabra is actually in Hebrew, which means "I will create as I speak".

Answer

J.K. Rowling answered in an interview why she used Avada Kedavra as the incantation for the killing curse. She answered that "It is an ancient spell in Aramaic which means “let the thing be destroyed”." so it is sort of the other way around to your interprettion regarding abracadabra.

There is a lot of Latin in the spells in your books Do you speak Latin?

Yes. At home, we converse in Latin. [Laughter]. Mainly. For light relief, we do a little Greek. My Latin is patchy, to say the least, but that doesn’t really matter because old spells are often in cod Latin—a funny mixture of weird languages creeps into spells. That is how I use it. Occasionally you will stumble across something in my Latin that is, almost accidentally, grammatically correct, but that is a rarity. In my defence, the Latin is deliberately odd. Perfect Latin is not a very magical medium, is it? Does anyone know where avada kedavra came from? It is an ancient spell in Aramaic, and it is the original of abracadabra, which means “let the thing be destroyed”. Originally, it was used to cure illness and the “thing” was the illness, but I decided to make it the “thing” as in the person standing in front of me. I take a lot of liberties with things like that. I twist them round and make them mine.

_{J.K.Rowling Official Site, Sunday 15 August 2004, J K Rowling at the Edinburgh Book Festival (Archived)}