— quintillionth , n. , adj.
/kwin til"yeuhn/ , n. , pl. quintillions , ( as after a numeral ) quintillion , adj.
n.
1. a cardinal number represented in the U.S. by 1 followed by 18 zeros, and in Great Britain by 1 followed by 30 zeros.
adj.
2. amounting to one quintillion in number.
[ 1665-75; quint ( us ) FIFTH + -illion (as in million ) ]