The Red Queen shook her head. You may call it 'nonsense' if you like, she said, but I've heard nonsense, compared with which that would be as sensible as a dictionary!
The Red Queen dismisses the idea that her words are nonsense, suggesting that what she considers nonsense is actually more logical than a dictionary. She implies that the previous statement or idea is so far-fetched that it surpasses typical nonsense in absurdity.
Her remark highlights her view that some notions may seem illogical or foolish, but in comparison, they might actually hold more sense than what is traditionally understood as sensible....