Anceps

In Greek and Latin meter, an anceps syllable is a syllable in a metrical line which can be either short or long. An anceps syllable may be called "free" or "irrational" depending on the type of meter being discussed.

Anceps syllables can be found in a variety of metrical forms. Anceps syllables in the middle or beginning of a line are characteristic of Aeolic meters, such as the Sapphic meter. These initial anceps syllables may reflect earlier Indo-European meters where only the last few syllables of a line were regulated. Anceps syllables are also found in the iambic trimeter of Greek drama.