There is no difference; they are synonyms.
A big difference
There is not a big difference between a Big Muff with tone wick and a original Big Muff. The only difference is the color.
the difference is this is small and that is big
The difference between brand position and a big idea is how a given advertising idea is placed.
It's not a very big difference but an iPad 3 is way better.
Eg.There is a big difference between night and day / everyone dresses differently
The big bang is a one off, the big bounce is cyclic.
The dodge big horn is a special edition ram. No true difference.
The difference between a big hotel and a small hotel is the amount of rooms that they have. The amount of staff and the size of the building are also differences.
The answer is 6000 cubic feet.
those are big words