My understanding is that this word means the same as "egad." If you look at how this word is used in the book, this makes sense.
"Egad" is an exclamation that originally came from the phrase "ye gods." So it is the sort of thing you say when you are surprised by something or you wish to exclaim about it for whatever reason.
In the book, you see such usages as "ecod, if you mind him..." This means something like "my goodness, if you pay attention to him..."
Another example is "Ecod! I'll not be made a fool of..." This means something like "by god, you're not going to make me look stupid."
So this interpretation of the word makes sense to me...