1) Minute fraction 2) Ordinal 3) Teeny-tiny fraction 
One trillionth is the reciprocal of a trillion, which means it has one of two definitions depending on whether the long scale or short scale numbering system is in use. ==Short scale countries== In most English-speaking countries, a trillionth is equal to 0.000 000 000 001, or 1 x 10−12 in scientific notation. The prefix for a number of this mag...
[adj] - the ordinal number of one trillion in counting order
adjective the ordinal number of one trillion in counting order