Late 18th century; earliest use found in John Stedman (1744–1797), army officer and author. Partly from rock + cod-fish, and partly from rock cod + fish.
Definition of rock codfish in US English:
rock codfish
nounˌrɒk ˈkɒdfɪʃ
rare
Rock cod 2.
Origin
Late 18th century; earliest use found in John Stedman (1744–1797), army officer and author. Partly from rock + cod-fish, and partly from rock cod + fish.