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Baron Rathcavan, of The Braid in the County of Antrim, is a title in the Peerage of the United Kingdom.^[1] It was created on 11 February 1953 for the Unionist politician Sir Hugh O'Neill, 1st Baronet. He had already been created a baronet, of Cleggan in the County of Antrim, on 17 June 1929 (see O'Neill baronets).^[2] O'Neill was the third son of Edward O'Neill, 2nd Baron O'Neill (see the Baron O'Neill for earlier history of the family) and the uncle of the Prime Minister of Northern Ireland Terence O'Neill, Baron O'Neill of the Maine. Lord Rathcavan was also a male-line descendant of Edward Chichester, 1st Viscount Chichester (see the Marquess of Donegall). He was succeeded by his eldest surviving son, the second Baron. He succeeded his father as Unionist Member of Parliament for Antrim in 1952, a seat he held until 1959, and was later a member of the Parliament of Northern Ireland. As of 2025^[update] the titles are held by his grandson, the fourth Baron, who succeeded in 2025.

The Honourable Sir Con O'Neill, second son of the first Baron, was a diplomat. His daughter Onora O'Neill, Baroness O'Neill of Bengarve, is a philosopher.

The family seat is Cleggan Lodge, near Ballymena, County Antrim.^{[citation needed]}

Coat of arms of Baron Rathcavan

Crest 1st an arm embowed in armour the hand grasping a sword all Proper 2nd a stork rising with a snake in its beak all Proper. Escutcheon Quarterly 1st & 4th per fess wavy the chief Argent and the base representing the waves of the sea in chief a dexter hand couped at the wrist Gules in base a salmon naiant Proper 2nd & 3rd chequy Or and Gules a chief Vair a mullet for difference. Supporters On either side a heron Proper standing on a billet fesswise wavy Argent charged with a bar wavy Azure. Motto Invitum Sequitur Honor; Lamh Dearg Eirin[5]