collude       
verb [ I ]  formal uk/kəˈluːd/ us/kəˈluːd/
 串通;勾结;共谋
to act together secretly or illegally in order to deceive or cheat someone
  It was suspected that the police had colluded with the witnesses. 警方涉嫌与证人暗中串通。 
 Synonym: conspire