The combination of literal and figurative meanings apply to Impromptu is a a lovely woman: a dangerous alliance.
Figurative language is when you use a word or phrase that does not have its normal, and literal meaning. In literal language, words do have the exact sense of their meaning.
In this case, a lovely woman would be a sweet woman, with a lot of sweet nothing. But then we have that a lovely woman means a dangerous alliance. If everything is pink color, then why would be a lovely woman a dangerous alliance? It's a good example of figurative meaning.
