# sleep with one eye open

> English word · Verb

## Definitions
1. To remain vigilant at all times, especially by remaining partially awake or sleeping only lightly so as to avoid being caught off guard.

## Etymology
Some animals sleep with one eye open, so as to remain alert to threats.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/sleep-with-one-eye-open