English definition of “swear”
/sweər/ verb (past tense swore, past participle sworn)
BAD LANGUAGE [I] › to use language which people think is rude or offensive: He was sent home because he swore at the teacher. She swore loudly and threw the box on the floor.
PROMISE [I, T] › to make a serious promise: [+ to do sth] I swear to tell the truth. [+ (that)] She swore that she was at home at the time of the accident.
TRUE [T] › used to say that you are sure something is true: [+ (that)] I could have sworn that she said she lived in Canterbury (= I was sure she lived in Canterbury, but now I have found that it is not true).