"I want to write down every exaggeration, half truth, fib, and bald-facer he utters, so I can gird my fury against him" p.389 Gone Girl
Could someone please explain the meaning of girding your fury against someone? Googling the word, I found that it commonly means to "get ready/prepare for a dangerous situation", but what does it mean in this context? The protagonist is not preparing for a dangerous situation and therefore I still feel perplexed. Is it perhaps an idiom?