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1. from Middle English sede ‘seed’; a metonymic occupational name for a gardener or husbandman, or a nickname for a small person.
2. from a late Old English personal name, Sida, a post-Conquest short form of compound names formed with sidu ‘custom’, ‘manner’; ‘morality’, ‘purity’ as the first element.

(Dictionary of American Family Names, Oxford University Press)
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