Weak kneed means lacking courage or confidence. The antonyms for weak-kneed are brave, courageous, fearless, determined, strong-minded, and self-assured. Being brave means having the ability to face danger, difficulty, or pain without being controlled by fear. Courageous is having the strength to do something in the face of danger or difficulty. Fearless means lacking fear, even when facing something dangerous or scary. Determined means showing firmness and strong will in achieving a goal. Being strong-minded means having a strong willpower and determination to face difficult situations. Finally, self-assured means feeling confident in one's abilities and self-esteem.