In this article, we inquire into the role played by language and core, politicized concepts in inter-professional coordination around expert work in transition. Empirically, we analyze how engineers and landscape architects cooperate around and compete for work related to rainwater management and climate adaptation in cities. We draw on qualitative empirical material, including around 30 in-terviews with involved professionals, focusing on the significance ascribed to the concept of "LAR", local drainage of rainwater, in the wider climate adaptation field since the 1990s. Using Andrew Abbott's (1988, 2005) theory of professions, we show how the story of LAR embodies a wider dynamic of 'proto-jurisdictional' emergence, with new professional roles and languages. Ab-bott places control over work tasks center stage in analyzing professional relations; and this includes 'ecological' considerations for how professions relate to political and academic institutions. On this basis, we show how professional actors use the specific LAR concept as a way of claiming compe-tence and forge alliances with others in the climate adaptation field. In reference to Abbott's notion of the 'knowledge systems' of professions, the implication we draw is that we need to understand professional languages in relation to broader jurisdictional struggles and translations between politi-cal and academic discourses.