Ó hAonghusa is the surname of at least two distinct Gaelic-Irish families. It is now anglicised as Hennessy and Hennessey.
One Ó hAonghusa family were located at Cill Bheagáin, in the Kingdom of Uí Failghe, in the Irish midlands.
Another family surnamed Ó hAonghusa were found at Ros Ailithir, in the Kingdom of Desmond. It is from this family that the founder of Hennessy brandy, Richard Hennessy of Mallow and Cognac (1720–1800), descended. Richard's descendant, Kilian Hennessy (1907–2010), was a French business magnate and one of the patriarchs of the Hennessy cognac company.