(n)sharing the risk by insurance companies; part or all of the insurer's risk is assumed by other companies in return for part of the premium paid by the insured
The Collaborative International Dictionary of English (GCIDE) v.0.53Collaborative International Dictionary (GCIDE)
n. 1. Insurance a second time or again; renewed insurance. [ 1913 Webster ]
2. A contract by which an insurer is insured wholly or in part against the risk he has incurred in insuring somebody else. See Reassurance. [ 1913 Webster ]