The term "weak-kneed" is used to describe someone who lacks strength or courage to face a challenging situation. The antonyms of "weak-kneed" would be words that describe individuals who are strong-willed, courageous, and capable of facing adversity. For example, the word "brave" is an excellent antonym for weak-kneed as it describes someone who is bold, daring, and has the courage to face danger head-on. Another antonym for weak-kneed could be "confident," which describes someone who is self-assured, has belief in their abilities, and can take on any challenge with ease. Other possible antonyms for weak-kneed include "hardy," "steadfast," "resolute," and "fearless.