This interesting surname originates from the Gaelic "Mac Giolla Seanain", which translates as "the son of (mac) the devotee (Giolla) of St. Senan", a name given to an Irish sept originating in Tyrone, but now equally well known in North Leinster. Curiously, the names "Leonard" and "Nugent" have been adopted as synonymous of Gils(h)enan, which is also found in the Anglicized form "Shannon" in County Fermanagh. The church register at Tottenham, London, records the marriage of one Rebecca Gilsenan to Thomas Eady on September 2nd 1804 while at St. Lukes, old Street, Finsbury London Edward Gilsenan married Elizabeth Crump on February 2nd 1806. At St. Botolph, Bishopsgate, London, Sarah Gilsenan married George Franklin on June 21st 1807. Richard and Mary Gilsenan had sons Joseph and Daniel, christened on April 14th 1816 and November 5th 1820, respectively at Weld Chapel, Southgate, London. On March 1st 1864 Catherine, daughter of John and Catherine Gilsenan was baptised at Lusk, Dublin. The first recorded spelling of the family name is shown to be that of James Gilshannon, marriage to Susan Brabazon, which was dated 1748, St. Peters, Drogheda, Co. Louth, Ireland, during the reign of King George 11, "The Last Warrior King", 1727 - 1760. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.