Word.ws English Dictionary

zero-day

zero-day adjective: of warez, released less than a day after the official product release.

Adjective

zero-day (not comparable)

  1. Of warez, released less than a day after the official product release.
    • Back then, having "zero day warez" (brand new cracked games that are not even one day old yet) on your BBS first was a big status symbol.2020, Oliver Markus Malloy, Bad Choices Make Good Stories
  2. (computer security) Of a vulnerability, newly discovered, and therefore still not fixed and possibly exploited by hackers or other criminals.
    • Although it's had tons of publicity, the IE zero-day vulnerability is so far only a real threat to people running IE6 on Windows XP, and you have to wonder about the competence of the companies actually affected by it[.]2010 January 18, Jack Schofield, “The IE zero-day vulnerability, Google, and you”, in The Guardian, →ISSN
    • Zero-day flaws are a burgeoning commercial field in the underground hacker economy where some gangs work to order for commercial or government clients which want to break into systems.2012 August 30, Charles Arthur, “Java exploit: Asian hackers behind first attacks, says Symantec”, in The Guardian, →ISSN
  3. (computer security) Of an exploit or its threat or an attack, benefiting from a newly found and yet unpatched or unmitigated flaw in software or hardware; using a zero-day vulnerability.
    • If your software is popular and has a high demand, you will want to defend against the "zero-day" cracker.2003, John Viega, Matt Messier, Secure Programming Cookbook for C and C++
    • Automatically creating reliable signatures of zero-day exploits is the focus of intense research efforts.2005, Valdes et al, Recent Advances in Intrusion Detection
  4. Used other than figuratively or idiomatically: see zero, day.
    • Average residues of 1.44 and 2.18 mg/kg chlortetracycline were seen in liver and kidney, respectively, at zero-day withdrawal.

Noun

zero-day (plural zero-days)

  1. (computer security) A vulnerability that has been discovered recently, and is yet unpatched or unmitigated; a zero-day vulnerability.
    • New Internet Explorer zero-day exploited in Hong Kong attacks
    • America’s National Security Agency (NSA) spends upwards of $25m in a year buying previously undisclosed security vulnerabilities – known as zero days, because that’s the length of time the target has had to fix them – but the large investment may not result in as much of a collection of hacking...2016 August 6, Alex Hern, “NSA denies ‘Raiders of the Lost Ark' stockpile of security vulnerabilities”, in The Guardian, →ISSN
  2. A day without obligations, where one does not worry about being productive.
    • Whatever you do, do not cut out the “zero days” as suggested in Joel Snape’s article on productivity tips (Big, beautiful goals – but can’t be bothered? 11 great productivity tips for lazy people, 10 July). These are days where you have no obligations, where you do not worry about being productive.2024 July 14, Christine Lehnen, “Why everyone should have ‘zero days’ and do the worst job first”, in The Guardian, →ISSN

Examples of zero-day in a sentence

  • The company says Mythos has revealed thousands of so-called zero-day—previously undiscovered—cyber vulnerabilities in every operating system and web browser, some of them up to 27 years old.2026 April 18, John Thornhill, “Lunch with the FT: Dario Amodei”, in FT Weekend (Life & Arts section), London: The Financial Times Ltd....
  • Before discussing ways to counter zero-day attacks, let's begin with the definition of what a zero-day attack is.2014, Michael Gregg, CASP CompTIA Advanced Security Practitioner Study Guide: Exam CAS-002:
  • Yet again, Adobe’s Flash plugin has been hit by a “zero-day” exploit, meaning that even users with a fully up-to-date installation of the software are vulnerable to attacks.2015 October 14, Alex Hern, “Flash hit by another zero-day vulnerability”, in The Guardian, →ISSN:
  • Plus: Cisco discloses a zero-day with no available patch, Venezuela accuses the US of a cyberattack, and more.2025 December 20, Andy Greenberg, “Hackers Stole Millions of PornHub Users’ Data for Extortion”, in Wired, San Francisco, Calif.: Condé...

Forms of zero-day

Adjective
alternative formzero day
alternative form0-day
Noun
pluralzero-days

Questions about zero-day

What does zero-day mean?
Zero-day means of warez, released less than a day after the official product release.
How do you use zero-day in a sentence?
The company says Mythos has revealed thousands of so-called zero-day—previously undiscovered—cyber vulnerabilities in every operating system and web browser, some of them up to 27 years old.
What part of speech is zero-day?
Zero-day can be an adjective or a noun.

Words near zero-day in the dictionary

  1. zero-based budgets
  2. zero-click
  3. zero-cool
  4. zero-coupon note
  5. zero-coupon notes
  6. zero-day
  7. zero-days
  8. zero-derivation
  9. zero-derivations
  10. zero-derive
  11. zero-derived

Source and license

Adapted from Wiktionary: zero-day (page history and authors). Text available under the Creative Commons Attribution-ShareAlike 4.0 license. Word.ws reformatted the entry and added links. Wiktionary data of 2026-09-02.

Last updated:

Pronunciation audio from Wikimedia Commons, each file under its own free license: En-au-zero-day.ogg.

Cite this entry: “zero-day.” Word.ws, https://word.ws/zero-day. Based on Wiktionary, CC BY-SA 4.0.