ElS - Don't spend too much time second-guessing the Qs.
They want to see you, not your interpretation of what you think they want to see/hear.
LHR -
When asked to define leadership at a commissioning Board interview what would you reply?
It probably won't come out in that form. They are much more likely to ask about a situation where you showed leadership, and how you dealt with the issues than ask you for a dictionary definition of a concept that people have written books about.