Is "Abner" (Allison) a nickname?

Abner is a very unusual first name in the Allison lines except for descendants of
Abner Allison (1769-1827) of Columbiana Co OH.There is a James Abner Allison, grandson of Halbert (Holbert) Allison of Augusta Co VA.Is Abner a nickname for William?Do "Abner's" come from England, Scotland or Ireland?