swear (EN)
verb

verb “swear”

swear; he swears; past swore, part. sworn; ger. swearing
  1. to use offensive words
    When he stubbed his toe, he couldn't help but swear loudly.
  2. to strongly assert (that something is true)
    He swore he had returned the book to the library on time.
  3. to make a serious promise
    She swore to keep her friend's secret no matter what.
  4. to take a legally binding oath
    Before the trial began, the witness swore to tell the truth, the whole truth, and nothing but the truth.