Derick Smith Thomson (Scottish Gaelic: Ruaraidh MacThòmais; 5 August 1921 – 21 March 2012) was a Scottish poet, publisher, lexicographer, academic and writer. He was originally from Lewis, but spent much of his life in Glasgow, where he was Professor of Celtic at the University of Glasgow from 1963 to 1991. He is best known for setting up the publishing house Gairm, along with its magazine, which was the longest-running periodical ever to be written entirely in Gaelic, running for over fifty years under his editorship. Gairm has since ceased, and was replaced by Gath and then STEALL. He was an Honorary President of the Scottish Poetry Library, and a Fellow of the Royal Society of Edinburgh and the British Academy. In June 2007, he received an honorary degree from Glasgow University.