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swear by someone or something
1. Lit. to utter an oath on someone or something. I swear by Jupiter that I will be there on time. She swore by her sainted mother that she would never do it again. The sheriff swore by his badge that he would lock her up if she ever did it again.
2. Fig. to announce one's full faith and trust in someone or something. I would swear by Roger any time. He is a great guy, and he tells the truth. I swear by this computer. It has always served me well.
1. Have great reliance on or confidence in, as in She swears by her personal physician. [Early 1800s]
2. Also, swear to. Have reliable knowledge of, be sure of, as in I think she was going to the library but I can't swear to it. [Mid-1700s]
3. Take an oath by, as in I swear by all the saints in heaven. [Early 1200s]
1. To have great reliance on or confidence in someone or something: He swears by his personal physician. She swears by the new computer program.
2. To have reliable knowledge of something; be sure of something: I think that's the person who stole my purse, but I couldn't swear by it.
3. To take an oath by something: I swore by all the angels and saints of heaven that I wouldn't reveal the secret to anyone.