An advisory service encounter brings together a domain expert with a layperson in a complex life situation. Because of the different backgrounds and expertise levels, the interlocutors and meanings is an essential part of advisory services and, generally, of expert-layperson collaboration. Establishing and maintaining a common lexicon is a specific and, at the same type, frequent type of collaborative work. Nevertheless, it remains unclear what efforts this collaborative work involves and what role collaborative IT applications play in this regard. A collaborative application can well support the maintenance of a common lexicon by providing a way to externalize terms or definitions. Or it can generate additional work by providing further terms and definitions to be incorporated in the common lexicon. That puzzle gets reflected in specific design dilemmas: should the system use expert or conventional terms, what is the source of the adequate terminology, to what extent should the system adapt to the individual lexical choices, etc. This manuscript explores the work involved in establishing and maintaining a common lexicon in advisory services between an expert and a layperson. In particular, it demonstrates how external material, a dedicated collaborative application developed for supporting advisory services, impacts the maintenance of a common lexicon. First, the manuscript depicts practices involved in translation and adoption of terminology from the system into the conversation. Second, it characterizes the system's impact on interlocutors' vocabulary. Overall, the study contributes to the discourse on expert-layperson collaboration by characterizing an important type of work, the vocabulary work, and by depicting the role of collaborative applications for this type of work.Abstract. An advisory service encounter brings together a domain expert with a layperson in a complex life situation. Because of the different backgrounds and expertise levels, the interlocutors require a common lexicon to guarantee for smooth collaboration. Consequently, the negotiation of terms and meanings is an essential part of advisory services and, generally, of expert-layperson collaboration. Establishing and maintaining a common lexicon is a specific and, at the same type, frequent type of collaborative work. Nevertheless, it remains unclear what efforts this collaborative work involves and what role collaborative IT applications play in this regard. A collaborative application can well support the maintenance of a common lexicon by providing a way to externalize terms or definitions. Or it can generate additional work by providing further terms and definitions to be incorporated in the common lexicon. That puzzle gets reflected in specific design dilemmas: should the system use expert or conventional terms, what is the source of the adequate terminology, to what extent should the system adapt to the individual lexical choices, etc. This manuscript explores the work involved in establishing and maintaining a common lexicon in advis...