Webster's Revised Unabridged Dictionary · 1913

Underwrite

Underwrite , transitive verb

1.
To write under something else; to subscribe. [Obsolete]
What addition and change I have made I have here underwritten. — Bp. Sanderson
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. — B. Jonson
The broker who procures the insurance ought not, by underwriting the policy, to deprive the parties of his unbiased testimony. — Marshall

Underwrite , intransitive verb

To practice the business of insuring; to take a risk of insurance on a vessel or the like.