In a somewhat long speech to Don Pedro, Benedick complains about what Beatrice had said to him. Benedick says that he felt like a target, and Beatrice was like a group of soldiers shooting at him. Benedick then adds the following:
She speaks poniards, and every word stabs. If her breath were as terrible as her terminations, there were no living near her, she would infect to the North Star. I would not marry her, though she were endowed with all that Adam bad left him before he transgressed. (216-20)
A poniard is a knife. Benedick felt like every word Beatrice spoke was a wound. He was hurt by her words. Of course, the wary reader will wonder why Beatrice's words hurt Benedick so much. If anyone else had made these comments about Benedick, he would not care nearly so much. Benedick is hurt because he cares so deeply in regards to what Beatrice thinks about him.
The word terminations also refers to Beatrice's words or speech. Benedick wittily jokes that if Beatrice's breath were as harmful as her words, she would pollute the entire sky. More important are the words that follow: "I would not marry her." No one has asked Benedick to marry her. The Prince did not bring up the subject of marriage. The idea of marriage comes from Benedick's own mind. He subconsciously is thinking about marriage -- with Beatrice.