un ‧ der ‧ write /ˌʌndəˈraɪt $ -ər-/ BrE AmE verb ( past tense underwrote /-ˈrəʊt $ -ˈroʊt/, past participle underwritten /-ˈrɪtn/) [transitive]
1 . formal to support an activity, business plan etc with money, and to take financial responsibility if it fails:
The government has agreed to underwrite the project with a grant of £5 million.
2 . technical if an insurance company underwrites an insurance contract, it agrees to pay for any damage or loss that happens
3 . technical to arrange to sell ↑ share s to ↑ investor s , and to agree to buy any which are not bought by them