In "The Legend of Sleepy Hollow," Washington Irving masterfully crafts an ambience of both nostalgic, rural beauty and superstitious creepiness. He primarily does so through the use of rich descriptions that employ unique diction. Take, for instance, the following passage (it's worth noting that the quotes in this response don't have page numbers because I used the online text provided by eNotes. Check it out by following my link at the bottom of this post):
Another of [Ichabod's] sources of fearful pleasure was to pass long winter evenings with the old Dutch wives, as they sat spinning by the fire, with a row of apples roasting and spluttering along the hearth, and listen to their marvellous tales of ghosts and goblins, and haunted fields, and haunted brooks, and haunted bridges, and haunted houses, and particularly of the headless horseman, or Galloping Hessian of the Hollow, as they sometimes called him.
Notice here Irving's rich use of language. The diction in the phrase "a row of apples roasting and spluttering along the hearth" immediately brings to mind a quaint, rural, autumn scene, and his use of the verb "spluttering" lends the passage a particularly dynamic tone. Additionally, the extensive folklore mentioned in this passage gives one the sense that Irving is drawing on well-established traditions of tale-telling and yarn-spinning, all of which make Sleepy Hollow feel like a real small town with its own histories and legends.
Contrast this description, which evokes the idealistically rustic qualities of the region, with the following passage toward the end of the story:
In the dark shadow of the grove, on the margin of the brook, [Ichabod] beheld something huge, misshapen and towering. It stirred not, but seemed gathered up in the gloom, like some gigantic monster ready to spring upon the traveller.
This is Ichabod's first encounter with the Headless Horseman, and it is suitably creepy. Notice Irving's diction here: words like "misshapen," "towering," "gloom," and "monster" immediately transport the reader to a frightening, nightmarish landscape, one that marks a strong contrast to the earlier passage, which was dominated by a safe, secure, and nostalgic tone. As such, it's clear Irving was a master craftsman when it came to word choice, as his precise use of diction creates an ambience that shifts from agreeably pastoral to ominous and frightening.