"short horizontal line placed over a vowel to indicate length," 1827, from Latinized form of Greek makron, neuter of makros "long" (from PIE root *mak- "long, thin").
Entries linking to macron
*mak-
*māk-, Proto-Indo-European root meaning "long, thin." It forms all or part of: emaciate; macro; macro-; macrobiotic; macron; meager; paramecium. It is the hypothetical source of/evidence for its existence is provided by: Greek makros "long, large," mēkos "length;" Latin macer "lean, thin;" Old Norse magr, Old English mæger "lean, thin."