1.  millionth(n = noun.linkdef) - position 1,000,000 in a countable series of things;
is a kind of rank

2.  millionth(n = noun.quantity) one-millionth - one part in a million equal parts;
is a kind of common fraction, simple fraction

   millionth(s = adj.all) - the ordinal number of one million in counting order;

   Being the last one of a million of units or objects counted in regular order from the first of a series or succession; being one of a million. [1913 Webster]

   The quotient of a unit divided by one million; one of a million equal parts. [1913 Webster]