One inevitable result of reading Sir Walter Scott is being exposed to words you haven't come across before. One recent example is 'umquhile'; it is a (now mostly obsolete) Scots word meaning 'late', in the sense of 'relatively recently deceased'. Very rarely it could be found in the variant, 'umwhile'.
I've mentioned before the struggles that Scottish philosophers in the early modern period had with trying to write in English; Scots and English were dialects much farther apart then than they have since become. Many of the differences were just ordinary dialectal differences arising from having populations that rarely interacted, but one of the more substantive differences was that Scots was much more directly influenced by legal language than English. This is the reason, for instance, why Scots then (and to a lesser extent even today) is a more latinate language than English -- Law-Latin was much more likely to contribute words to everyday vocabulary in Scotland than in England. But it wasn't just Latin in particular; 'umquhile' is from Middle English (originally meaning 'sometime' as an adjective, and loosely related to the later term 'erstwhile'), but was also primarily used in legal contexts; it's thus unsurprising to find the Scots using it in the early modern period.
As time has gone on, a few Scottish words have entered into English, but the general pattern has been for Scots to shift to accommodate English grammar and vocabulary. This is unfortunate, I think, as a general matter; but it's one of the historical reasons why anyone still reads David Hume today -- his historical works were popular among the English, and had a reputation of being a very readable, if occasionally eccentric, summary of English history. Writing in English rather than Scots in a popular niche with relatively little competition kept Hume's name alive. And Hume himself was aiming at it -- it's why he started spelling his name 'Hume' rather than the more correct 'Home', so that the English would pronounce it in a way that was approximately right.
Sir Walter Scott, like Robert Burns, is at an interesting position in all of this. Burns and Scott also often wrote in English for English audiences, but they both were trying to contribute as well to Scottish literature itself. As such, they have become major figures in the preservation of some of the vernacular Scots of their day, maintaining a significan proportion of Scots while being readable to those who read English rather than Scots. This balancing act must have been immensely difficult, especially in the early years of the Union, but both, in different ways, manage to do it very well. Scots is only a shadow of its former self, but it is a shadow of its former self; it has so far, even if only through hanging by its fingertips, avoided becoming the umquhile Scots language.
