Aboriginal Australians are celebrated for their use of linguistic devices to mark the subtleties of social situation and relationship. Three sorts of phenomenon are widely reported (see Capell 1962; Dixon 1972: 19): (1) special vocabulary is often associated with male initiation (see, for example, Hale 1971); (2) there is often extensive word tabooing, usually involving strict prohibition on names of deceased people, as well as on words that sound like such names (for examples of such practices across Cape York Peninsula, see Roth 1903); and (3) many societies have so-called ‘Mother-in-law’ languages – special vocabularies that replace all or part of the normal lexicon in speech between kin who stand in certain avoidance relationships to one another. Prototypically across the continent, a man must avoid his own mother-in-law. Such vocabularies have been reported from widely separated areas, but the most detailed and best-known descriptions involve languages of North Queensland (see Thomson 1935; Dixon 1971, 1972). The material I discuss in this paper is of the last type and comes also from Cape York Peninsula.