In Co. Clare, the homeland of the MacNamaras, the name is very numerous. In fact in everyday speech it is usually abbreviated to simple Mac: this is interesting, because another Mac name, MacMahon, comes first in the numerical list of Co. Clare names, considerable ahead of MacNamara, which has second place, yet the abbreviation is never applied to MacMahon. The sept of MacNamara was, after the O'Briens, the most important and powerful of the Dalcassians of Thomond. They were hereditary marshals to the O'Briens and had the privilege of inaugurating the chief of the O'Briens who was, of course, often a king. The sept was originally confined to a small territory, but by the end of the eleventh century they had become lords of Clancullen (which comprises a great part of East Clare) and they are so described by the Four Masters many times at various dates between 1099 and 1600. The sept in due course became two-the chief of West Clancullen (barony of Bunratty) being MacNamara Fyne (i.e. fionn, fair), and the chief of East Clancullen (baronies of Upper and Lower Tulla) MacNamara Reagh (i.e. riabhach, swarthy or grizzled). They were to a great extent dispossessed in the Cromwellian debacle, but one family, resident until quite lately at Ennistymon, became Protestants and were extensive landlords up till the Land Act of 1903. The history of Clare is full of the name MacNamara : among other notable acts they founded the Franciscan Abby of Quin in 1402.
  After a period of obscurity they emerged into fame or notoriety in the eighteenth century. Donough MacNamara (d. 1814), better known by the Gaelic form of his name-Donnchadha Rua Mac Conmara-was born at Cratloe in East Clare, educated as a priest, expelled, led a wild life and is one of the best known of the Gaelic poets. His contemporary, another Clareman, Admiral James MacNamara (1768-1826) was tried for murder following a duel over a dog and was acquitted. Thomas "Fireball" MacNamara was a duellist pur sang, whose career in France is reminiscent of the "three Musketeers"; he eventually became a highwayman as well as a Clare rebel and ended on the scaffold about the year 1710. Two other MacNamaras were noteworthy in France at the time of the French Revolution, particularly Count MacNamara, naval commander and diplomatist, who was assassinated in 1790 on account of his royalist sympathies. For a note on the name of the well-known playwright Brinsley MacNamara see page 47.
  MacConmara, the Irish form of this name, is derived from the words cu (hound) and na mara (of the sea). The forename Cumara was at one time found in connexion with the surname MacConmara, and was the name of the eponymous ancestor of the sept, who was twenty-third in decent from Cormac Cas.
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  Sept describes a group of persons who or whose immediate and known ancestors bore a common surname and inhabits the same locality.
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  Oddly enough in County Clare though MacMahon considerably outnumbers MacNamara it is invariably the latter which is indicated by the use of ordinary parlance of the plain Mac as an abbreviation: indeed so usual is this that it is often written in the abbreviated form, generally with the addition of the K-Mack.
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From the book IRISH FAMILIES Their Names, Arms and Origins, by Edward MacLYSAGHT, Allen Figgis : Dublin 1972