1) Ordinal 
One billionth is the reciprocal of a billion, which means it has one of two definitions depending on whether the long scale or short scale definition is being used. ==Short scale countries== In most English-speaking countries, a billionth is equal to 0.000 000 001, or 1 x 10-9 in scientific notation. The prefix for this number is nano, and is abbr...
[adj] - the ordinal number of one billion in counting order 2. [n] - (in the U.S.) position 1,000,000,000 in a countable series of things
adjective the ordinal number of one billion in counting order