I'm curious if there's any cases of a word that originated in English (didn't come from a foreign source) replacing another word in every day usage?
One example: Old English lið has been replaced by limb, both of native origin. This Wikipedia page has a bunch of such examples of obsolete words, though most of the replacement words are from other languages.
Something like thou? You is the form which has replaced the archaic thou.
The word withershins is rarely used anymore, it is the same as counter-clockwise or anti-clockwise, both with Latinate origin, both still English words.
In the U.S., doughnut (first OED citation 1809) replaced the Dutch-origin word olykoek (first OED citation 1795). For olykoek, a 1740 calque [translation] oily cake is cited, so the word olykoek may have been in use well before doughnut.
This first OED citation for doughnut is
D. Knickerbocker, Hist. N.Y. An enormous dish of balls of sweetened dough, fried in hog's fat, and called doughnuts, or olykoeks.