"U-238 is also fissionable. U-235 is fissile, however, which means a neutron with no additional velocity will cause it to fission.
Close. Fissile materials will undergo fission with any velocity neutron."
Isn't that what I wrote?
You wrote "a neutron with no additional velocity will cause it to fission". While this is technically true, it is also true that "a neutron with additional velocity will cause it to fission".