The insistently articulated lexicon that surrounds the Morte Darthur's numerous references to betrayal communicates a powerful concern with treason and its relationship to the chivalric community. Criticism assessing the Morte Darthur's key words and concepts has attended to the rhetoric of ideals and their role in discourses of community. Jill Mann provides an inventory of crucial terms central to understanding connections between knights: ‘aventure, worship, body, departe, hole, togidir, felyship’. Following Elizabeth Archibald's elucidation of Malory's ideal of fellowship, recent scholarship has deepened our understanding of how communities within the Morte are shaped. These approaches have, however, focused primarily on the positive ideals themselves, without remarking upon the explicit centrality of antithetical manifestations such as treason to the definition and development of these ideals. Moreover, critics who have sought to analyze Malory's attitudes towards treason have not devoted sustained attention to the words that express these attitudes, thereby leaving unaddressed thys langayge's implications for understanding the values the text promotes, to whom it promotes them, and the methods by which it does so. The persistent, emphatic articulation of ‘treson’ and ‘traytour’ in Malory's text, particularly in direct discourse, constitutes a distinct departure from his sources that has, to my knowledge, gone unremarked. This article aims to assess how treason, as a key word and concept, functions with respect to the Morte and its textual intentions; that is, how Malory's representation of treason contributes to processes of community formation both diegetically and in fifteenth-century England.