As applied linguists know very well, how we use language both constructs and reflects our understanding. It is therefore important that we use terms that do justice to our concerns. In this presentation, I suggest that a more apt designation than "multilingual" or "second language acquisition" (SLA) is "multilingual" or "second language development" (SLD). I give a number of reasons for why I think SLD is more appropriate. Some of the reasons that I point to are well known. Others are more current, resting on a view of language from a complex systems perspective. Such a perspective rejects the commodification of language implied by the term "acquisition", instead imbuing language with a more dynamic quality, implied by the term "development", because it sees language as an ever-developing resource. It also acknowledges the mutable and interdependent norms of bilinguals and multilinguals. In addition, this perspective respects the fact that from a target-language vantage point, regress in learner performance is as characteristic of development as progress. Finally, and most appropriately for AILA 2011, the term "second language development" fits well with the theme of the congress--harmony in diversity--because it recognizes that there is no common endpoint at which all learners arrive. For, after all, learners actively transform their linguistic world; they do not merely conform to it.