I believe that the name Thompson is in all likely hood only one of hundreds of variant names stemming from the Gaelic name of "MacTamhais". "Mac", means "son of" and "Tamhais" means, "Thomas". So with Thompson or Thomson you have "Thomas's son". The "mh" in the middle of MacTamhais is pronounced as a "v". MacTamhais was later slightly more anglicised to the name MacTavish. See the Official Clan MacTavish/Thom(p)son Web Site to understand more at:-
NOTE: We are not a sept to Clan Campbell as they will dispute. Clan MacThomas I believe have their origins based in Clan MacTavish. I have no doubt that they may dispute that too. I do accept that Clan MacThomas is a recognised clan in it's own right and can claim some Thompson's and Thomson but I still believe they are a brother clan to Clan MacTavish. That is my opinion. I do agree that one does have to do some serious research to find the facts. I hope anyone searching does find those facts. Clan MacTavish/Thompson has been without a chief for 200 years since the Battle of Culloden. So for 200 years there was no chief to put the lies and mistakes to rest. Many, but not all have changed their surname spelling due to the Highlander Clearances and many had to flee as I believe did mine from the English to Ireland. It was used as a jump point to Canada, America, Australia, New Zealand and other places around the world (many did stay in Ireland). Contact the Chief of Clan MacTavish/Thom(p)son at firstname.lastname@example.org
Follow the URL's and you will find a great deal of information and learn much. Enjoy.