Old English changed the inner vowels of a lot of words to change their tense or meanings. Sometimes this was because the ending made it harder to say in some ways or because noises blended together.
Here’s a good longer article on this
https://dannybate.com/2022/03/17/of-mouses-and-mans-the-origins-of-englishs-vowel-swapping-nouns-and-verbs/
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