duodecillion
noun
duo·de·cil·lion ˌdü-ō-di-ˈsil-yən 
ˌdyü-
often attributive
US : a number equal to 1 followed by 39 zeros see Table of Numbers
also, British : a number equal to 1 followed by 72 zeros see Table of Numbers
Word History
Etymology
Latin duodecim twelve + English -illion (as in million)
First Known Use
1844, in the meaning defined above