To clarify what I mean, take the following imaginary conversation:

Less Wronger: Hey! You seem smart. You should consider joining the Less Wrong community and learn to become more rational like us!
Normal: (using definition: Rationality means using cold logic and abstract reasoning to solve problems) I don't know, rationality seems overrated to me. I mean, all the people I know who are best at using cold logic and abstract reasoning to solve problems tend to be nerdy guys who never accomplish much in life.
Less Wronger: Actually, we've defined rationality to mean "winning", or "winning on purpose" so more rationality is always good. You don't want be like those crazy normals who lose on purpose, do you?
Normal: No, of course I want to succeed at the things I do.
Less Wronger: Great! Then since you agree that more rationality is always good you should join our community of nerdy guys who obsessively use cold logic and abstract reasoning in an attempt to solve their problems.

As usual with the motte and bailey, only the desired definition is used explicitly. However, the connotations with the second mundane use of the word slip in.