Probably alteration of musk deer (influenced by mousefrom its small size)
American Heritage Dictionary of the English Language, 5th Edition
Mouse-deer Sentence Examples
The Asiatic elephant; the seladang, a bison of a larger type than the Indian gaur; two varieties of rhinoceros; the honey bear (bruang), the tapir, the sambhur (rusa); the speckled deer (kijang), three varieties of mouse-deer (napoh, plandok and kanchil); the gibbon (ungka or wawa'), the siamang, another species of anthropoid ape, the brok or coco-nut monkey, so called because it is trained by the Malays to gather the nuts from the coco-nut trees, the lotong, kra, and at least twenty other kinds of monkey; the binturong (arctictis binturong), the lemur; the Asiatic tiger, the black panther, the leopard, the large wild cat (harimau akar), several varieties of jungle cat; the wild boar, the wild dog; the flying squirrel,.
The so-called Spectre Huntsman of the Malay Peninsula is said to be a man who scours the firmament with his dogs, vainly seeking for what he could not find on earth - a buck mouse-deer pregnant with male offspring; but he seems to be a living man; there is no statement that he ever died, nor yet that he is a spirit.
The third group is that represented by the chevrotains or mouse-deer, forming the family Tragulidae, with Tragulus in south-eastern Asia and Dorcatherium (or Hyomoschus) Tragullna.
Other species include the hog deer (C. porcinus), the barking deer or muntjac (Cervulus muntjac), and the chevrotain or mouse deer (Tragulus meminna).
Three or four species of deer are common, including the mouse-deer, or plandok, an animal of remarkable grace and beauty, about the size of a hare but considerably less heavy.