coinsurance n1 : joint assumption of risk (as by two underwriters) with another
2 : insurance (as fire insurance) in which the insured is obligated to maintain coverage on a risk at a stipulated percentage of its total value or in the event of loss to suffer a penalty in proportion to the deficiency
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.