- Lest is a conjunction in English that is used to say that if we don’t do something, there is a possible negative or unpleasant outcome. You could replace lest with ‘for fear that.’ Take a look at these sentences:
Helen turned the radio down lest she should miss the phone ringing. (Macmillan dictionary)
Stay out of sight, lest we be discovered! (notice the use of the English subjunctive here!)
The editors of the Metro are saying that if we don’t remember and commemorate all those who died and sacrificed their lives on 11 September, we risk forgetting the significance and importance of that day.
Front page of Metro taken from http://www.newseum.org/todaysfrontpages/