This story is told by Golightly Family Researcher Jeanne Nix Bundy:

"William "the Lion" Canmore - King of
Scotland married and they had children.
William had a child named Henry Canmore -
named Golightly, because he escorted the
House of Gollaighlaigh (mercenary soldiers
of King of Scotland) to Ireland to fight the
Normans. Although I cannot prove that Henry was indeed a Canmore, but our relative in Ireland certainly believes he was, it would
appear that the Gaelic for special soldier to
the King or rather House of Galloighlaigh
stayed attached to this name and was down
through his line referred to as Henry Golightly, Gelately, or Golitely. There was another Golightly, the grandson of his Henry that ran for office in England - where I would imagine he moved and married and English woman.

The Golightly crest was designed in Scotland by the House of Ghalloglaigh, a close family of the King of Scotland in the 12th century. The family history of the House of Ghalloglaigh is related by Jim Gollogley, Esquire of Dublin, Ireland, a Golightly descendant.

Mr. Gollogley states that the Gaelic of Gollogley (Golightly), which was the Irish language of the time, was "Mac An Ghalloglaigh," meaning "Son of the Foreign Soldier." Mr. Gollogley declares this translation derives from the 12th century where the King's mercenary soldiers from the House of Ghalloglaigh in Scotland were hired by Irishman, mostly farmers, in County Donegal to help them fight the Normans who came to Ireland from England. There is a town in Donegal called Milford, which is known in Gaelic as "Baile An Ghalloglaigh," meaning home of the Ghalloglaigh's, (Golloagley's/Golightly's/Gellately's. The Golightly crest is displayed above. The motto of the Golightly's is: "Hitherto Unconquered" or 'HACTENUS INVICTUS", because of the defeat of the Normans in Donegal, Ireland at the time.