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. 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

Consumers naturally looked for the cheapest flight — and airlines wanted to position themselves as having the lowest fare lest they literally fall off the screen as a consumer scrolled through options.

From MarketWatch • Apr. 10, 2026

In the mid-19th century, do-gooders such as William Alcott and Sarah Josepha Hale began urging children be fed a bland diet, lest rich flavoring imperil their health and futures.

From The Wall Street Journal • Feb. 20, 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

One of our weird quirks is we don’t always laugh as loudly as we would with a normal audience, lest we influence anyone else’s opinion about whether a movie is funny.

From Los Angeles Times • Jan. 31, 2026

I’ll make it fast, lest Mama or the little ones catch me and start to holler.

From "The Detective's Assistant" by Kate Hannigan