underwriter

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that underwrites, especially.
• noun A person or firm engaged in the insurance business.
• noun An insurance agent who assesses the risk of enrolling an applicant for coverage or a policy.
• noun One that guarantees the purchase of a full issue of stocks or bonds.
• noun A sponsor, as of a television show.

from The Century Dictionary.

• noun One who insures, or carries on a business of insurance, especially of marine insurance.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who underwrites his name to the conditions of an insurance policy, especially of a marine policy; an insurer.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An entity assuming a financial risk.
• noun A person working for an insurance company who arranges and authorizes an insurance policy with a broker or insured.
• noun finance An entity undertaking to market newly issued securities.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an agent who sells insurance
• noun a financial institution that sells insurance
• noun a banker who deals chiefly in underwriting new securities