lest

American  

[lest] / lɛst /

conjunction

1. for fear that; so that (one) should not (used negatively to introduce a clause expressive of an action or occurrence requiring caution).

   He kept his notes by his side lest faulty memory lead him astray.

2. that (used after words expressing fear, danger, etc.).

   There was danger lest the plan become known.

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idioms

1. lest we forget. see lest we forget.

lest British  

/ lɛst /

conjunction

1. so as to prevent any possibility that

   he fled the country lest he be captured and imprisoned

2. (after verbs or phrases expressing fear, worry, anxiety, etc) for fear that; in case

   he was alarmed lest she should find out

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Etymology

Origin of lest

First recorded before 1000; Middle English leste, contraction of the lesse the, thi les the; late Old English the lǣste, earlier thȳ lǣs the, literally, “whereby less that” ( thȳ instrumental case of the demonstrative and relative pronoun, lǣs less, the conjunction)

Example Sentences

Speak out for them now, lest there be no one left to speak for you.

From The Wall Street Journal • Apr. 7, 2026

At one point housewives were admonished not to shake their dust mops outdoors lest that contribute to smog.

From Los Angeles Times • Mar. 26, 2026

He promiscuously puts his name on everything this side of the moon, and I probably shouldn’t even mention that particular satellite, lest he get ideas.

From Slate • Feb. 16, 2026

In both cases, the outside world was careful not to investigate what was taking place, lest it be forced to act.

From The Wall Street Journal • Feb. 9, 2026

I had wrapped this thread around my finger and was pulling on it as gently as I could, lest it break.

From "Beyond the Bright Sea" by Lauren Wolk