Here are some options:
For physical strength:
* Might: Implies powerful force or potential.
* Power: Refers to the ability to exert force or control.
* Force: Refers to strength that can be used to move or change something.
* Muscles: Refers to the physical source of strength.
For mental or emotional strength:
* Resilience: Ability to recover from difficulties.
* Determination: Firmness of purpose.
* Courage: Facing fear or danger.
* Willpower: Ability to control one's actions and impulses.
For abstract strength:
* Strength: This is the most general and direct term.
* Potency: Refers to strength or effectiveness.
* Vigor: Refers to energy and vitality.
The best noun for you will depend on the specific context and what aspect of strength you want to emphasize.