The term 'KIND OF SERUM' can be solved by the crossword solution 'TRUTH' (5 letters). A serum is a type of medical product that is used to treat or prevent diseases. It is typically made up of proteins, antibodies, or other substances that are injected into the body. Serums can be used to treat a variety of conditions, including allergies, infections, and cancer. The term 'KIND OF SERUM' could refer to any type of serum, but the crossword solution 'TRUTH' suggests that it is specifically referring to a truth serum, which is a type of serum that is used to induce truth-telling in people who are suspected of lying.