'Macron' definitions:

Definition of 'macron'

(from WordNet)
noun
A diacritical mark (-) placed above a vowel to indicate a long sound

Definition of 'Macron'

From: GCIDE
  • Macron \Ma"cron\, n. [NL., fr. Gr. ? long.] (Pron.) A short, straight, horizontal mark [-], placed over vowels to denote that they are to be pronounced with a long sound; as, [=a], in d[=a]me; [=e], in s[=e]am, etc.
  • Syn: macrotone. [1913 Webster]