Recorded in many spellings as shown below, this is an ancient Irish surname. It derives from the pre 10th century Gaelic O' Glasain or O' Gliasain. The prefix O' indicates male descendant of, to which was added the personal name Glasain. This is from "glas" literally meaning green, but used here in the sense of inexperienced. The clan belonged to the ancient territory of Mac Ui Bhriain Aradh, an area that lay between Nenagh and Lough Derg on the border of County Tipperary. The nameholders were of the same stock but not apparently the same origin, as the O'Donegans, whose name derives from the Gaelic word 'donn' meaning brown or dark. In the census of Ireland in 1659 the surname under the various spellings such as O' Glasane, Glason, Glasson, Gleeson, Glisane, Glison, Glisson, Gleasane, and Glassane, is well recorded in conjunction with O' Donegan in Counties Tipperary, Clare and Limerick. Father William Gleeson of Irish stock was called the "founder of the Catholic church in California". The first recorded spelling of the family name is shown to be that of Teag O' Glissane. This was dated 1590, in the "Records of Extensive Landowners in County Tipperary", during the reign of Queen Elizabeth 1, known as "Good Queen Bess", 1558 - 1603. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.