catflap.org Online Dictionary Query

  challenge a witness /tʃˈalɪndʒ ɐ wˈɪtnəs/
  die Glaubwürdigkeit eines Zeugen anzweifeln [jur.]
   see: challenge sth., contest sth., impugn sth., impeach sth., challenging, contesting, impugning, impeaching, challenged, contested, impugned, impeached, challenge the accuracy of a statement, The new data challenges many old assumptions., Children challenge their parents' authority far more nowadays than they did in the past.