十万八千里
one hundred and eight thousand li — an extremely long distance
e.g. 相差十万八千里
be poles apart
e.g. 就学问而论，我比他差了十万八千里。
In terms of knowledge (or scholarship), I am miles behind him.
e.g. 孩子的世界与成人的世界不啻十万八千里。
The child's world is vastly different from that of the adult.
