E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A fawning, mean-spirited fellow, a crop-tailed dog (latin, curtus, crop-tailed. French, court; our curt). According to forest laws, a man who had no right to the privilege of the chase was obliged to cut off the tail of his dog. Hence, a degenerate dog or man is called a cur.