The term RELATIVE OF A HADDOCK can be solved by two crossword solutions: COD (3 letters) and HAKE (4 letters). COD is a type of fish that is related to the haddock, and is found in the Atlantic, Pacific, and Arctic oceans. HAKE is another type of fish that is related to the haddock, and is found in the Atlantic and Pacific oceans. Both COD and HAKE are popular seafood items, and are often used in dishes such as fish and chips.