Armstrong is a surname of Scottish borders origin. It derives from a Middle English nickname which meant someone with strong arms. In Ireland the name was adopted as an Anglicization of two Gaelic names from Ulster: Mac Thréinfhir (meaning 'son of the strong man') and Ó Labhradha Tréan (meaning 'strong O'Lavery'). Clan Armstrong is a clan from the border area between England and Scotland. The Scottish Armstrong is reputed to have been originally bestowed by "an antient (sic) king of Scotland" upon "Fairbairn, his armour-bearer" following an act of strength in battle.
From the name Ó Labhradha Tréan (meaning 'strong O'Lavery' and sometimes written in AngloIrish as "Tréanlámagh") the following surnames survive: "Trainor", Traynor", O'Lavery", "O'Laverty", "McLavery", "McLaverty", MacLavery" and "MacLaverty". Although the name "Armstrong" is quite common in the Aghagallon and Glenavy area of County Antrim in Northern Ireland the other names are to be found within the 9 Ulster Counties and Scotland especially along the west coast.
manual translation of Wikipedia sources into WeRelate sources