This is the 4679th most frequent Japanese word.
断固
Firmly; resolutely; adamantly.
Here, '断固' is used to describe someone's firm and unwavering determination in defending their opinion.
彼は断固として彼の意見を守った。
He firmly defended his opinion.
In this sentence, '断固' conveys the necessity for resolute and determined action.
我々は断固たる行動が必要だと感じた。
We felt that decisive action was necessary.
The term '断固' here reflects a strong and resolute refusal or rejection.