Madness vehemently resists definition and is rather inscribed with meaning in each of its different cultural and historical contexts. Attempts to understand madness have been made by clerics, physicians, psychologists, and laypeople alike, but still the condition refuses to be explicitly determined. The ambiguity of madness plays an important role in Shakespearean tragedy, as his mad characters reveal their mental state in differing physiological and psychological expressions. Not only have critics and readers of these plays been invited to interpret the madness of Shakespeare’s characters, but agents within the play are also set as interpreters. Those who attempt to ‘read’ madness in Macbeth are Lady Macbeth’s waitinggentlewoman and her doctor, and Macbeth’s noblemen, whose thoughts are voiced by Menteith.1 In Othello, Iago establishes Othello’s condition of excessive jealousy as mental insanity, so he is both a catalyst to the latter’s madness and an interpreter; Desdemona, Cassio, and Emilia are other, passive interpreters of madness in the play. 2 Using the Lexicon of Early Modern English, this essay will explore the etymology and lexicology of language used by non-mad agents to describe or diagnose madness in Macbeth and Othello. Reading words in their Early Modern usage reveals rich nuances in meaning, thereby inscribing new meaning onto the condition of madness and how it functions within the plays. In Macbeth and Othello, the language of interpreting madness is necessarily ambiguous and varying, enforcing wider themes of uncertainty and disorder within the texts.