valko- (“white-”) + häntä- (“tailed”) + kauris (“any small and slender deer such as roe deer”); coined in 2008 by a committee that made a proposal for Finnish names of all mammals. This animal was and still is commonly called valkohäntäpeura. The problem is, according to the committee, that peura without any modifiers refers "reindeer" whereas kauris refers to roe deer and other small, slender deer.
Declension of valkohäntäkauris (type vieras)
This term is gaining ground e.g. among zoologists and in media, but valkohäntäpeura still appears to be more commonly used (in 2011) by the general public.