reionization
/riːˌʌɪənʌɪˈzeɪʃn/(also reionisation)
noun
1 Physics. The action of ionizing something for a second or further time; an instance of this.
2 Astronomy. The ionization of neutral hydrogen atoms formed during recombination in the early universe (108 to 109 years after the Big Bang). Frequently attributive Compare recombination.
Origin
Early 20th century. From re- + ionization. Compare slightly later reionize.