What is a short, straight, horizontal mark [-], placed over vowels to denote that they are to be pronounced with a long sound; as, a, in dame; e, in seam, etc called?

macron — A short, straight, horizontal mark [-], placed over vowels to denote that they are to be pronounced with a long sound; as, a, in dame; e, in seam, etc. (Webster's 1913.)

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