Sky noun - The expanse of air surrounding the earth.
Usage example: the sky usually looks deep blue on a bright clear day
Welkin is a synonym for sky in heavens topic. In some cases you can use "Welkin" instead a noun "Sky", when it comes to topics like high. literary substitute
Both words in one sentence
- Almost every time the sky comes up in Frigid Winds And Burning Hearts, it's described with the word "welkin".
Source: Author Vocabulary Calendar
Google Ngram Viewer shows how "sky" and "welkin" have occurred on timeline