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English definition of “swear”

swear

verb [I or T] (PROMISE)    /sweər/ US  /swer/ (swore, sworn)
B2 to promise or say firmly that you are telling the truth or that you will do something or behave in a particular way: I don't know anything about what happened , I swear (it). [+ (that)] You might find it difficult to believe , but I swear (that) the guy just came up to me and gave me the money .informal She swore blind (= promised definitely ) (that) she didn't know what had happened to the money . [+ to infinitive] New gang members must swear to obey the gang leaders at all times . In some countries , witnesses in court have to swear on the Bible . I swore an oath to tell the truth , the whole truth , and nothing but the truth . A few of us knew what was going to happen , but we were sworn to secrecy (= we were made to promise to keep it a secret ). I think his birthday is on the 5th, but I wouldn't/couldn't swear to it (= I am not completely certain about it).Making and breaking promises and commitments
(Definition of swear verb (PROMISE) from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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