The bottom surfaces of shoes or feet, or plural of sole (a type of flat fish).
From Old French 'sole' meaning bottom (from Latin 'solea' meaning sandal/sole). The fish meaning came later because of the fish's flat sole-like shape, and shoe soles were named by analogy.
The flatfish called sole got its name because it's literally as flat as a shoe sole—medieval people were great at naming things based on what they physically looked like, so language tells stories about ancient observations.
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