The name of a valley about three miles to the north-east of Makkah, where in the eighth year of the Hijrah a battle took place between Muhammad and the Banu Hawazin, when the latter were defeated. In the Qur’an, the victory of Hunain is ascribed to angelic assistance.
Surah ix. 25: “Verily God hath assisted you in many battle-fields and on the day of Hunain.”
Based on Hughes, Dictionary of Islam