Supplement (with) is a term that can be used to describe the action of adding something to an existing item or situation. The crossword solutions for this term are ADD (3 letters), LARD (4 letters), and ATTACH (6 letters). ADD means to join or combine two or more things together, while LARD means to ADD fat or oil to food to make it richer or more flavorful. Finally, ATTACH means to fasten or connect one thing to another. All three of these words can be used to describe the action of supplementing something with an additional item.