Altered short form of William, not used before the 19th century. The reason for the change in the initial consonant is not clear, but it conforms to the pattern regularly found when English words beginning with w- are borrowed into Gaelic. The nickname ‘King Billy’ for William of Orange is an early example from Ireland, which may have influenced English usage. It is bestowed occasionally as a name in its own right.
English and eastern German: occupational name for someone who was employed at a lodging house or infirmary, from agent derivatives of Middle English spital, Middle High German spital, spittel ‘lodging house’, ‘infirmary’.