A person or thing considered to be strong, powerful, or difficult to defeat. They say the young boxer is a force to be reckoned with, so I'm betting he'll win the match tonight.The attorney may look petite and meek, but she's a force to be reckoned with in the courtroom.
Fig. someone or something that is important and powerful and must not be ignored. Walter is a force to be reckoned with. Be prepared to deal with him.The growing discontent with the political system is a powerful force to be reckoned with.