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There's probably a word I've been pronouncing wrong my whole life that I don't know about
(discuss.tchncs.de)
A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. The best ones are thoughts that many people can relate to and they find something funny or interesting in regular stuff.
Both Oxford English Dictionary and Merriam-Webster agree that "nitch" was the correct pronunciation in both British and American English until very recently. You already linked Merriam-Webster, so here's O.E.D:
(N.E.D is the original name of the O.E.D. "/nɪtʃ/" is pronounced "nitch" and /niːʃ/ is pronounced "neesh".)