Single-handed (adjective)

1. Done or achieved with only one hand or by oneself.
2. Done or achieved without help or assistance.

Origin:

Middle english (in the sense "with one hand"): from single + handed.

Examples:

1. He single-handedly built the house.
2. She single-handedly won the game.
3. He was able to fix the car single-handedly.
4. She single-handedly managed the company.
5. He single-handedly completed the project.