Final answer:
The word that shares a similar meaning to 'extraordinary' as used in the sentence is 'marvelous'.
Step-by-step explanation:
The word that shares a similar meaning to the word extraordinary as used in the sentence is marvelous. Both words convey the idea of something exceptional, remarkable, or out of the ordinary. In this context, Mandela is referring to an extraordinary human disaster, which means an extremely severe or uncommon disaster that lasted for a prolonged period of time.