[koh-in-shoo r-uh ns, -shur-]
  1. insurance underwritten jointly with another or others.
  2. a form of property insurance in which an insurer assumes liability only for that proportion of a loss which the amount of insurance bears to a specified percentage of the value of the property.
    1. a form of health insurance in which the insured party contributes a specified percentage of the total cost of medical expenses after a deductible has been reached.
    2. the percentage contributed by the insured party: My coinsurance is 20%.Compare copay.

Origin of coinsurance

First recorded in 1885–90; co- + insurance Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for coinsurance


  1. a method of insurance by which property is insured for a certain percentage of its value by a commercial insurance policy while the owner assumes liability for the remainder
  2. joint insurance held by two or more persons
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012