Definition of swear by phrasal verb from the Oxford Advanced Learner's Dictionary

 

swear by

 phrasal verb
phrasal verb
 
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Phrasal Verbs

    swear by somebody

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    swear by something

     
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  1. 1to name somebody/something to show that you are making a serious promise I swear by almighty God that I will tell the truth.
  2. 2(not used in the progressive tenses) to be certain that something is good or useful She swears by meditation as a way of relieving stress.
See the Oxford Advanced American Dictionary entry: swear by