Webster 1913 Edition
Not avoidable; incapable of being shunned or prevented; inevitable; necessary;
Not voidable; incapable of being made null or void.
hemorrhage produced by the afterbirth, or placenta, being situated over the mouth of the womb so as to require detachment before the child can be born.
Webster 1828 Edition
1.That cannot be made null or void.
2.Not avoidable; not to be shunned; inevitable; as unavoidable evils.
3.Not to be missed in ratiocination.