1.To write under something else; to subscribe. "What addition and change I have made I have here underwritten."
2.To subscribe one's name to for insurance, especially for marine insurance; to write one's name under, or set one's name to, as a policy of insurance, for the purpose of becoming answerable for loss or damage, on consideration of receiving a certain premium per cent; as, individuals, as well as companies, may underwrite policies of insurance. "The broker who procures the insurance ought not, by underwriting the policy, to deprive the parties of his unbiased testimony."