Legislatures enact laws and the courts interpret them. Under the doctrine of legislative supremacy, a judge is not free to ignore or modify a statutory provision in order to substitute a rule that seems to him to be better reasoned; thus where the language of a statute is clear and unambiguous, interpretation is unnecessary and it must be enforced according to its terms. Nevertheless, gaps and ambiguities can arise and, in such cases, courts apply interpretive rules, or ‘canons of construction’, (...) to resolve these ambiguities. One frequently invoked rule requires that words that are not defined by a statute be given their ordinary meaning by the interpreting court. In recent years, the United States Supreme Court has increasingly relied upon dictionary definitions in applying this rule. The Court’s use of dictionaries as authority for its interpretations incorporates the assumption that the dictionary is the best source for ascertaining the meaning of statutory texts. This article challenges that assumption on linguistic grounds. I argue that the focus on definitions skews the interpretation of statutory language by isolating words from their semantic context. By comparing two cases in which the Court used dictionary definitions to a third case in which the definition used by the Court was contained in the statute itself, I demonstrate that the ordinary meaning of legal terms cannot be determined by dictionary definitions. (shrink)