This article focuses on how Grade 6 students interactionally make meaning out of subject-related language encountered in civics textbook material by searching for synonyms and engaging in discussions. Employing ethnographically-inspired methods, data was collected through observations and audio recordings of civics teaching in two linguistically diverse classrooms in which the students were taught in the majority language, Swedish. In the article, oral classroom interaction is perceived as a crucial part of the meaning-making social practice in which students' disciplinary literacy is developed. Key analytical concepts are discursive shifts and discursive mobility - the ability to move between and within different discourses. The results show that the use of online dictionaries promoted decontextualizing processes in which the students unsuccessfully tried to negotiate multiple abstract meanings that, in many cases, were unrelated to the disciplinary content. In other exchanges, the adults gave interactional support by contextualizing the words and expressions in content-relevant ways and pointing out recognizable parts of words. In some cases, the teacher instead drew attention to words that have different meanings, which complicated the content-relevant understanding of the words. Implications for working with subject-related vocabulary in ways which support rather than hinder disciplinary understanding are discussed.