An Etymological Dictionary of the German Language/Renntier
Renntier, n., ‘reindeer,’ ModHG. only, from the equiv. Swed. ren, which is derived from OIc. hreinn (AS. hrân), whence also Du. rendier, E. reindeer; from the same source probably are Ital. rangifero, Fr. rangier (and renne), ‘reindeer.’ OIc. hreinn is usually considered to be a Finn. and Lapp. loan-word (raingo).