Wikipedia
Aonghas is a masculine given name in Irish and Scottish Gaelic. It is composed of Celtic elements meaning "one", and "choice". A variant spelling of the Scottish Gaelic name is Aonghus. The Irish form of the Scottish Gaelic names is Aengus. A pet form of the Scottish Gaelic names is Angaidh, which is represented in English as Angie, pronounced "an-ghee".
The earliest form of the given name Angus, and its cognates, occurs in Adomnán's Vita Columbae (English: "Life of Columba") as Oinogusius, Oinogussius. This name likely refers to a Pictish king whose name is recorded variously as Onnust, Hungus. According to historian Alex Woolf, the early Gaelic form of the name, Oengus, was borrowed from the British Pictish Onuist, which appears in British as Ungust. Woolf noted that these names are all derived from the Celtic *Oinogustos. Linguist John Kneen derived this name from two Celtic elements the following way: *Oino-gustos, meaning "one-choice". Woolf also stated that between about AD 350 and AD 660, the Insular Celtic dialects underwent changes which included the loss of the final syllables and unstressed vowels, which affected *Oinogustos thus: *Oinogustos.