perispomene
The circumflex ⟨◌͂⟩, a diacritical mark used in the polytonic script of Greek.
The perispomene (῀) is an accent like any other, on syllables originally long.
Where it comes from
From Ancient Greek περισπωμένη (perispōménē).
Adapted from the Wiktionary entry perispomene (CC BY-SA 4.0).