In this article, we analyze how linguistic terms have been borrowed and reinterpreted across disciplines. Specifically, we describe how terminology associated with Applied Linguistics (AL) changed meaning as it entered the new disciplinary context of Writing Studies (WS), often resulting in confusion and turbulence between the two fields. As in other work on the History of English (HEL), our analysis thus considers how language change works both over time (diachronically) and across different communities of speakers (synchronically). Our analysis of how the terms code-switching, translingualism, translanguaging, and declarative and procedural knowledge have been used and defined in AL versus WS points to the disciplines' different value systems. We argue that such differences in usage may also stem from WS's need to establish itself as a discipline. We end by considering how WS and AL, informed by HEL, can work together to further our knowledge of language and language-centered pedagogy.