What is "swithun"

Swithun (or Swithin, , ; died 862 AD) was an Anglo-Saxon bishop of Winchester and subsequently patron saint of Winchester Cathedral. His historical importance as bishop is overshadowed by his reputation for posthumous miracle-working. According to tradition, the weather on his feast day (15 July) will continue for forty days. The precise meaning and origin of Swithun's name is unknown, but it most likely derives from the Old English word swiþ, 'strong'.