noun
plural trillion or trillions
[count] the number 1,000,000,000,000 :one thousand billion
a trillion
and one [=1,000,000,000,001]
a trillion
and a half = 1.5 trillion [=1,500,000,000,000]
a very large amount or number
Brit old-fashioned :the number 1,000,000,000,000,000,000 :one million million million