Fortitude is the power to resist attack; strength; firmness.

Fortitude is that strength or firmness of mind which enables a person to encounter danger with coolness and courage, or to bear pain or adversity without murmuring, depression, or despondency; passive courage; resolute endurance; firmness in confronting or bearing up against danger or enduring trouble.

Synonyms:

Courage; resolution; resoluteness; endurance; bravery.