Ó hÁdhmaill is a Gaelic Irish clan from Ulster.^[7] The name is now rendered in many forms, most commonly Hamill. The clan are a branch of Cenél nEógain (specifically, Cenél mBinnigh), belonging to the Uí Néill; they claim descent from Eochu Binneach, the son of Eógan mac Néill. Their descendants in Ireland are found predominantly across Ulster, and County Louth, Leinster.

In Irish if the second part of the surname begins with a vowel 'Á', the form Ó attaches a h to it, this is the h-prothesis mutation. In this case Ádhmaill becomes Ó hÁdhmaill. The other forms effect no change: Ní Adhmaill, (Bean) Uí Adhmaill.^[8][9]

Capitalized as: Ó hÁDHMAILL or Ó ʜÁDHMAILL, the first 'h' should always be either lowercase, or a smaller 'H' font size.

The Motto is Esse Quam Videri, translated as To Be Rather Than To Seem.^[10]

The Slogan (battle cry) is "Vestigia nulla retrorsum", translated as No backward steps.^[11]

The Coat of Arms is described as being; A shield azure field with two horizontal bars of ermine fur. On top of the shield is a ducal coronet. Atop the coronet is the figure of a leopard in profile, sitting with its face to the viewer's left.^[10][11]

• The Azure/Blue represents Strength, Loyalty and Truth
• The Ermine is associated with the robes and crowns of Royal and Noble Personages
• Ducal Coronet is a crown of a duke
• Leopard in profile is traditionally depicted the same as a lion

One of the leading clans of the Cenél mBinnigh, Cenél nEógain a branch of the Northern Uí Néill. They are descendants of Eochach Binnich mac Eógain, son of Eógan mac Néill, son of the fifth-century Néill Noígiallaig (Niall of the Nine Hostages), founder of the Uí Néill dynasty. Cenél mBinnigh where the first clan of the Cenél nEógain (Cenél nEóghain)^[12] to advance from Inishowen.

The O'Hamills continued to move from North Ulster with the Northern Ui Neill's, and ruled territory in County Tyrone and County Armagh, South Ulster.^[3]

• Hereditary Chief or Clan chief; Ua hAghmaill (O'Hamill), Teallach Duibhbrailbe.
• Cinéal (Kinship); Cenél nEógain (Cinel Eoghain).
• Finte (Clans); Ua Brolaigh, herenaghs of Tech na Coimairce and Clongleigh.
• Branches;
  • Cenél mBinnig Glinne in the valley of Glenconkeine, barony of Loughinsholin
  • Cenél mBindigh Locha Droichid east of Magh Ith in Tirone (County Tyrone)
  • Cenél mBindigh Tuaithe Rois and one branch of the Ua Brolaigh, east of the River Foyle and north of the barony of Loughinsholin

Prior to the middle of the 20th century, Irish was usually written using the Gaelic typefaces, in this case the surname appeared as Ó hÁḋmaıll. The dot above the lenited letter (ḋ) was replaced by the letters dh from the standard Roman alphabet changing it to Ó hÁdhmaıll. Also the Irish language makes no graphemic distinction between dotted i and dotless ı so at the same time it changed to Ó hÁdhmaill.

As the dh is silent, the pronunciation is similar to spelling it as O'Hamill which is how it came to be spelt when it was phonetically anglicised,^[13] over time the spelling lost the O' and changed to Hamill,^[14] giving us the modern Irish-English spelling of Hamill.

• Hamill Surname List
• Hammill Surname List

• Hamill, South Dakota

While Hamell in Irish is spelt Ó hÁmaill,^[33] it is often incorrectly used as the Irish version of Hamill.^[23][32]

There are several surnames that are spelt the same but are unrelated:^{[34][35][3][36]}

• Some Scottish Hamill's are of Norman origin and are named after a location; Haineville or Henneville in Manche, France. Which itself was named from the Germanic personal name Hagano and the Old French ville for 'settlement'.
• The English Hamill's of Saxon origin are named after a nickname from Middle English, and the Old English "hamel".
• The English/Scottish Hamilton's are named after a location; the village of Hamilton, Leicestershire, England.

• Finte na hÉireann (Clans of Ireland)