Lest definitions

lĕst
For fear that.

Tiptoed lest the guard should hear her; anxious lest he become ill.

conjunction
19
0
For fear that; in case; so that . . . not.

Speak low lest you be overheard.

conjunction
17
0
So that someone or something not; in case someone or something might.
conjunction
16
1
That.

Afraid lest he should fail us.

conjunction
14
1
Lest is defined as something done in order to avoid an undesirable consequence.

An example of lest is when you bring an umbrella in order to avoid getting wet.

conjunction
6
0
For fear that; that . . . not; in order that . . . not; in case.

He won't go outside, lest he be eaten by those ravenous eagles.

conjunction
0
0
That (without the negative particle); - after certain expressions denoting fear or apprehension.
conjunction
0
0

Origin of lest

c.1200, contracted from Middle English phrase les te "less that," from Old English phrase þy læs þe "whereby less that," from þy, instrumental case of demonstrative article þæt "that" + læs (see less) + þe "the." The þy was dropped and the remaining two words contracted into leste. (http://www.etymonline.com/index.php?term=lest)