One of the Medieval English names for the Polecat (Mustela putorius) was ‘foulmart’, a name that dates back at least to the 14th century (Onions, 1966). The species is considered to be native to Wales and to the rest of Britain, or at least its native status does not appear to be in question. However, it is one of three long-established and well-recognized mammal species in Wales whose Welsh name does not have a Celtic origin. The Rabbit (Oryctolagus cuniculus), the Fallow Deer (Dama dama) and the Polecat all have Welsh names of English or French derivation, respectively, cwningen, danas and ffwlbart. The first seems to derive from the Middle English (14th century) konyng, the second from the Old French (pre-13th century) dain, whilst the last appears to derive from foulmart (Thomas, 1966). Aybes & Yalden (1995) used British place name evidence to substantiate a number of claims regarding the past status of the Wolf (Canis lupus) and Beaver (Castor fiber). Since Celtic British, or its daughter language Welsh, has been in continuous use in the British Isles from the beginning of Iron Age times to the present day, whereas the earliest form of English only appeared in the 5th century, the provenance and derivations of Welsh words for our fauna and flora should reveal more about the status within these islands of the organisms that they represent than their English counterparts. The nomenclature of the Polecat has intrigued me for some years. How could a supposedly native mammal have acquired a Welsh name of English origin, especially in view of the fact that the Welsh words for the other small mustelids, Weasel (Mustela nivalis) (gwenci), Stoat (Mustela erminea) (carlwm) and Pine Marten (Martes martes) (bele), are all Celtic in origin, or of obscure origin? Could the fact that the other two introduced species have borrowed names indicate that the Polecat is also introduced (or at least reintroduced after a prolonged absence)? There could be a simple linguistic explanation for the adoption of a new name, such as the ambiguity of an earlier name. Or it may be by a purely sociolinguistic process that the name changed under foreign influence, just as modern Breton, for example, has lost the Celtic plural kon ‘dogs’ and uses instead the loanword chas (containing the same base as the French word for hunting). There could, however, be an ecological explanation for the change. Was the Polecat present in Britain at all during the first millennium? Could the Polecat have been a late Medieval introduction, perhaps either for harvesting Rabbits or for its pelt? Could our modern wild Polecat be in fact a feral reversion-to-type from introduced early ferret-type stock? The answers to these questions must hinge not only on linguistic inferences, but also on documentary or subfossil evidence that might show that the Polecat is both a natural postglacial colonist and has enjoyed continuous and unbroken occupation of some part of the Mammal Rev. 2002, Volume 32, No. 2, 145–149. Printed in Great Britain.