In Great Expectations, Chapter 57, what does "a cool four thousand" mean?

In context, it is necessary to look at the various definition of cool. The dictionary defines the use of the word 'cool' in terms of sums of money, distances, etc., emphasizing their largness. As a result, we can infer that the speaker is trying to express that this is a VERY large sum of money. Something like; 'no less than four thousand pounds'.