in a ... guise

1. 以……的外表
   He is an enemy in a friendly guise.

   他是个装扮成朋友的敌人。

in the guise of

1. 装扮成
   A man appeared at the castle gate in the guise of a woodcutter.

   有个人装扮成樵夫的样子出现在城堡大门口。

under the guise of

1. 假借
   A lot of nonsense was talked, under the guise of philosophy.

   假借哲学的名义讲了一大堆的废话。