Unthank is an interesting name: there are a few hamlets/small villages named Unthank in the North of England; there's even an Unthank Hall. However, I suspect that more people live in Norwich's Unthank Road than in all of the other places put together.
According to Ancestry, the meaning derives from Old English unthanc ‘without consent’, i.e. a squatter’s holding.
Chart showing the number of references in each month of the diary’s entries.