plimsoll: [20] The British politician and social reformer Samuel Plimsoll (1824–98) was one of the leading instigators of the Merchant Shipping Act 1876. Amongst its provisions was that a line should be painted round the hulls of ships to indicate a safe limit for loading. This was Plimsoll’s idea, and it became known as the Plimsoll line. It is thought that the word plimsoll was applied to ‘gym shoes’ in allusion to the line running round the shoes formed by the rubber welt or trimming.
Plimsoll (n.)
"mark on the hull of a British ship showing how deeply she may be loaded," 1881, from Samuel Plimsoll (1824-1898), M.P. for Derby and advocate of shipping reforms (which were embodied in the Merchant Shipping Act of 1876). Sense extended 1907 to "rubber-soled canvas shoe" (equivalent of American English sneakers) because the band around the shoes that holds the two parts together reminded people of a ship's Plimsoll line; sense perhaps reinforced by sound association with sole (which sometimes influenced the spelling to plimsole). The name is of Huguenot origin.