American English

Definition of swear to phrasal verb from the Oxford Advanced American Dictionary

 

swear to

 phrasal verb
phrasal verb
 
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Phrasal Verbs

swear to something

(informal)
 
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to say that something is definitely true I think I put the keys back in the drawer, but I couldn't swear to it (= I'm not completely sure).
See the Oxford Advanced Learner's Dictionary entry: swear to