Helping or encouraging someone to do something wrong or illegal.
From Old French 'abeter' meaning 'to set a dog on someone,' later evolving to mean 'to incite or encourage wrongdoing.'
The phrase 'aid and abet' is redundant legally—'abet' means to encourage, while 'aid' means to help, so saying both is like saying 'help help,' but courts repeat it for emphasis in criminal charges.
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