unˈderwrite transitive verb

1. To write (something) beneath
2. To subscribe to (a statement, etc)
3. To accept the risk of insuring
4. To guarantee to take, or find others to take (certain shares, under certain conditions)
5. To write too little about
6. (reflexive) to write below the level of which one is capable, not to do (oneself) justice
7. To sign one's name beneath (obsolete)
8. To subscribe (one's name; obsolete)
9. To agree to (Shakespeare)

To practise as an underwriter

unˈderwriter noun

1. Someone who practises insurance business, esp in ships
2. Someone who underwrites share issues, etc

unˈderwriting noun