Second to die life insurance - A form of insurance, traditionally used as an estate planning tool, that pays a death benefit only upon the death of the insured who survives the longest. Its main purpose is to pay estate taxes upon the death of the second insured. Because it is based on joint life expectancy, its premium is less than the total premiums for individual policies on the same lives. This type of insurance is available in many forms, including policies with interest-rate features and flexible premiums. .