The term BITTERN refers to a type of wading bird that is related to herons and egrets. It is typically found in marshy areas, and is characterized by its loud, booming call. The crossword solutions for the term BITTERN are HERON (5 letters), EGRET (5 letters), and MARSH (5 letters). All three of these words are related to the BITTERN, as it is a type of HERON, is closely related to egrets, and is usually found in marshy areas.