Definify.com

Webster 1913 Edition

Noun.

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

Noun.

One who insures; an insurer; so called because he underwrites his name to the conditions of the policy.

underwriter ‎(plural underwriters)

An entity assuming a financial risk.
A person working for an insurance company who arranges and authorizes an insurance policy with a broker or insured.
(finance) An entity undertaking to market newly issued securities.
They were the underwriters of the company's shares, but only on a "best efforts" basis.