in a reinsurance policy, the aggregate amount that the insurer must retain before anything is paid by the reinsurer; for example £200,000 XS £100,000 with an aggregate retention of £500,000 means that a £150,000 loss would erode £50,000 of the aggregate; once the aggregate has gone, the reinsurance policy begins paying out, subject to the excess.
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Total (limit of indemnity, premium, retention etc).
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The greatest amount recoverable on account of a single loss or during a policy period, or on a single project.