Over time, languages evolve and change depending on the context in which they are being used. From Old English to Middle English, and from there to Modern and Contemporary English, many words have changed and taken new meanings and sounds.
Words do some truly inventive things when they change, and change they always do.
Some switch their sounds around, like when hros became hors, nowadays spelt with an extra e as horse.
Some lose their sense of having an internal composition, like when wāl-hros ‘whale-horse’ became walrus.
Erich Round lists some more words that have switched their sounds through time. Read about them on Morph.
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