oh! I'm pretty sure lilac flowers are edible, (make sure to clean them if you use) maybe make sure just in case? Double checking won't do any harm. I've heard that you could soak them in water and then drink it?
They are associated with a nymph from Greek mythology I think,, her name is Syringa. She turned herself into a lilac bush to escape Pan because he had frightened her.
Also I've heard it can be connected to spirituality and the third eye chakra because of it's color!
Good luck I hope you can make use of it, they are lovely flowers,