n. (pl. same or (in sense 3) trillions) 1 a million million (1,000,000,000,000 or 10(12)). 2 (formerly, esp. Brit.) a million million million (1,000,000,000,000,000,000 or 10(18)). 3 (in pl.) colloq. a very large number (trillions of times). °Senses 1-2 correspond to the change in sense of billion. trillionth adj. & n.
[ F trillion or It. trilione (as TRI-, MILLION), after billion ]