E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
I will beat thee like a stockfish. Moffet and Bennet, in their Healths Improvement (p. 262), inform us that dried cod, till it is beaten, is called buckhorn, because it is so tough; but after it has been beaten on the stock, it is termed stockfish. (In French, etriller quelquun, a double carillon, to a pretty tune.)
Peace! thou wilt be beaten like a stockfish else.Jonson: Every Man in his Humour, iii. 2.