Nonillion is a number that is equivalent to a million million million million million million million million. However, there are different words that you can use as synonyms for nonillion. This includes decillion, undecillion, duodecillion, tredecillion, quattuordecillion, quindecillion, sexdecillion, septendecillion, octodecillion, novemdecillion, and vigintillion. These words are used to represent numbers that are greater than a quadrillion. While these numbers may not often come up in everyday conversations, knowing their synonyms can be useful in scientific or mathematical contexts. Moreover, it helps to improve a person's vocabulary and knowledge of numbers.