in a ... guise

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

   他是個裝扮成朋友的敵人。

in the guise of

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

   有個人裝扮成樵夫的樣子出現在城堡大門口。

under the guise of

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

   假借哲學的名義講了一大堆的廢話。