Sidwell

From an English surname of uncertain origin, possibly originally a habitational name from an unidentified place with a second element from Old English well(a) ‘spring’, ‘stream’, but on the other hand early forms are found without prepositions. It has been used as a given name on occasions since at least the 16th century. In the case of the female saint (Latin: Sativola), a cephalophoric martyr venerated in Exeter, Devon, England, it is an anglicized form of Sadfyl, possibly influenced by the word well. (According to the legend, when Sidwell was beheaded with a scythe, a holy well miraculously sprang up from the ground where her head fell.)
It may also be a phrasal nickname.