My first guess would be that it is an independent clause. This is just a single statement.
Answer:
While grammar schools focused on Latin rhetoric, drama was also included. He probably left school at fourteen to undertake an apprenticeship of seven years until his coming of age.
Explanation:
I believe the word means being cautious in this context.
Try 'No Fear Shakespeare' on Sparknotes there is an updated and translated version of Macbeth
