It is an Anglicised form of the Irish and Scottish Gaelic name Aonghas (also spelt Aonghus), which is composed of Celtic elements meaning "one" and "choice".
Short forms of the name include Gus, which may be lengthened to Gussie, and Irish Naos.
[1] Angie (/ˈæŋɡiː/ ANG-ghee; Scottish Gaelic: Angaidh) is a common pet form of the name.
[1] According to historian Alex Woolf, the early Gaelic form of the name, Oengus, was borrowed from the Pictish Onuist, which appears in British as Ungust.
[3] Linguist John Kneen derived this name from two Celtic elements the following way: *Oino-gustos, meaning "one-choice".