Tredecillion is an incredibly large number, equivalent to 10 to the power of 42. There are a few synonyms for this astronomical number, including one googol, which is 10 to the power of 100, a decillion trillion, which is 10 to the power of 39, and a quattuordecillion, which is 10 to the power of 45. Other massive numbers include septuagintillion, which is 10 to the power of 81, and googolplex, which is 10 to the power of a googol. These numbers are often used in scientific or mathematical calculations, but they are so immense that they are difficult to comprehend in practical terms.