Used to represent the so called sonus medius, a short vowel sound between U and I before labial consonants in Latin words such as ⟨OPTͰMUS⟩ for optumus and optimus, later used as a variant of Y in inscriptions for Greek upsilon (as in ⟨OLͰMPICUS⟩ for Olympicus), possibly inspired by an early form of the spiritus asper.
