Every now and then - usually when talking with an older individual or someone from the United States Midwest or South - I hear the word "spell" used to mean a short period of time, such as: "Come sit down and rest a spell." I've also heard it used as a verb, like, "When Pete arrives he will spell Tito, who has been working since dawn."
What is the history and origins of this meaning and use of the word spell? And is it a colloquialism or can it be used in more formal settings?