The field of rhetoric has generated studies of definitional disputes and of the relationship between definition and power. Informed by the idea of collective definition created over time, these studies raise an important theoretical-practical question about definition and contestation that may be approached through a concept of authority. Etymologically, authority precedes or transcends power and is rooted in the twin poles of creativity and reason. Accordingly, this essay proposes a rhetorical manner of contesting definitional authority that performs immanent critique. The manner is warranted by analysis of a 1971 essay that challenged psychiatry's authority to define "homosexuality." (Contains 100 notes.)