a. Happening at the same instant. C. Darwin. [ 1913 Webster ]
n. [ Co- + insurance. ] Insurance jointly with another or others; specif., that system of fire insurance in which the insurer is treated as insuring himself to the extent of that part of the risk not covered by his policy, so that any loss is apportioned between him and the insurance company on the principle of average, as in marine insurance or between other insurers. [ Webster 1913 Suppl. ]