Old Irish
Old Irish was the Goidelic language in the Middle Ages. People spoke Old Irish in Ireland, before the year 1000 AD. Old Irish was a Goidelic language, and modern Goidelic languages like Irish and Scots Gaelic came from it.
People speaking Insular Celtic languages probably first came to Ireland at the start of the Iron Age, about 500 BC. By around 500 AD, people in Ireland all had the same Goidelic language and culture. Speakers of Old Irish began to move to Britain as Britain became weaker. Other peoples of Britain named these people the Scot.
Old Irish was the only language in the Goidelic languages until Old Irish split into the modern Goidelic languages of Irish, Scots Gaelic, and Manx. These languages are Insular Celtic languages and part of the bigger group of Celtic languages.
References
Celtic languages
Languages of Europe