The spelling of "didst vanishing act" may seem confusing for English learners, but it follows the rules of Early Modern English. "Didst" is the second person singular past tense of "do" and is pronounced as /dɪdst/. "Vanishing" is the present participle of "vanish" and is pronounced as /ˈvænɪʃɪŋ/. "Act" is a noun indicating a performance and is pronounced as /ækt/. Together, the phrase refers to the theatrical disappearance of someone or something. While this usage is no longer common, understanding the spelling and pronunciation can enhance one's understanding of the evolution of the English language.