The phrase "dost on the sly" means to do something secretly or covertly. The spelling of "dost" follows Middle English verb conjugation and is pronounced as /dʌst/. The "o" is written as pronounced, and the "s" is added to indicate it's the second-person form. The word "sly" is spelled as pronounced, with the /aɪ/ diphthong, and is an adjective to describe how the action is being done. Together, the phrase offers a peek into Shakespearean-era English and its unique grammar and vocabulary.