The term 'Boilermaker Ingredient' is a reference to the popular alcoholic beverage known as a Boilermaker. This drink consists of a shot of whiskey dropped into a glass of BEER. The crossword solutions for this term are BEER, which is a 4 letter word. BEER is an alcoholic beverage made from fermented grains such as barley, wheat, and rye. It is one of the oldest and most widely consumed alcoholic drinks in the world. BEER is a key ingredient in the Boilermaker, and is essential for making this classic drink.