The Turkic and Mongol words in William of Rubruck's Journey (1253-1255)
Larry Clark, Indiana University, Journal of the American Oriental Society, vol.93, No 2, (Apr.-June., 1973), pp 181-189.
p.189
...With tumen our survey is completed, and a summary of our identification can be made. The following words are only Turkic: ayran, *kam, karakumis, kumis, soyur, su, yam, yastuk. One could also add to this list the words kulan and kurut, but the fact is that these were early borrowed by the Mongols, so that Rubruck need not have recorded them as Turkic. Also to be considered is the ambiva