No difference. The reason why legal terms are always said twice is that USA inherited both England and France terms.
That's why it's :
Assault AND Battery
Aid AND Abet
One is English, the other French.
What does 'abet' mean exactly? The word derives from the French 'abeter' - to hound, which itself derives from the Norse 'beita' - to cause to bite.
The phrase 'aid and abet' was coined in the late 18th century, by which time the term 'abet' had lost its original 'cause to bite' meaning