The ultimate origin of pig is a bit of mystery. One would expect a word like pig to appear in Old English and have a common Germanic root; the expected form would be *picga or *pigga. But the word does not appear in the extant Old English manuscripts, except in one case, the compound picbred, pig-bread or food for pigs. There is also a 12th century surname of Pigman, which may be related.
The common Germanic root for the animal is swin, or swine as we use it today. This word is common in Old English, while *picga is vanishingly rare. There are also no cognates in other Germanic languages, unless one counts the Dutch big, which also means pig. But the shift from /p/ to /b/ between English and Dutch does not follow any known phonetic pattern. A /p/ in English should remain a /p/ in Dutch. So this just adds to the confusion about the word.
Copyright 1997-2015, by David Wilton