Irish and Scottish Gaelic, it turns out, has a brother. Manx Gaelic is spoken on the Isle of Man. Though the last native speaker of the language died in 1974, there has been a revival of late for the language including a grammar school that teaches entirely in Manx.
Manx began to separate from Irish Gaelic in the 13th century and Scottish Gaelic in the 15th century. By the mid 19th century, there were few, if any, native speakers of Manx who spoke no English. In 1874, the English scholar of Celtic languages, Henry Jenner estimated that 30% of the Manx population spoke the language on a regular basis while the 1901 census showed that only 9.1% of the Manx could speak the language. By the 1921 census, the number had dropped to 1.1%. However, because of the resurgence in the language, the 2001 census revealed that 2.2% of the 76,000 citizens have some ability to speak Manx.
As a language, most of the words are derived from Old Irish and Irish and Scottish Gaelic, but some words are derived from Old Norse, Latin, Anglo-Norman French and Middle and Modern English.
Interestingly (maybe not for you, but for me), one of the people who was instrumental in the mid 20th century in the upkeep of the language was Eamon De Valera who was one of the key members of the Irish resistance against the British in 1916 and had a long political career in Ireland after the revolution and later civil war.**