Lynch is an Irish name. The original Gaelic version was Loingsigh or Loingseach, meaning mariner or seafarer. The name is common to the Galway area in the west of Ireland. O'Loingsigh would mean "descendant of the mariner or seafarer."
Elizabeth Lynch wrote that in the 9th and 10th centuries, some tribes used surnames, but in the 11th and 12th centuries, Brian Boru made an ordinance that every family and clan should adopt a particular surname. Many chose an ancient chief.
"The name Lynch is derived from Longseach, a mariner. Maion, afterwards called Labradh Longseach, was son of Oiloll Aine, son of Laeghare Lorc, son of Ugaine Mor or Hugony the Great. Labradh Longseach, 70th monarch, BC 541, wore the crown of Ireland for eighteen years and fell at the last by the sword of Cobhthach Caolmbreag."
Elizabeth Lynch, The Lynch Record; NY: William J. Hirten Co., 1925, p. 19
The Lynch coat of arms from the Galway tribe is a blue background on the shield with a gold chevron set between three gold clover leafs. (La Reina Rule and William K. Hammond, What's in a Name; NY: Jove/HBJ, 1973.)