guardrail

noun

guard·​rail ˈgärd-ˌrāl 

variants or less commonly guard rail

plural guardrails also guard rails

1

: a railing that protects (as by preventing people from falling)

The sidewalk … is separated from the heavily treed ravine by a guardrail.

—Jack Lakey

especially : a barrier placed along the edge of a highway at dangerous points

The car swerved and hit a guardrail.

2

guardrails or less commonly guard rails plural : protections against something undesirable : safeguards

Whatever the reasons for defaults, housing observers are most concerned that the guardrails put in place after the housing crisis are no longer there to help.

—Andrea Riquier

often, specifically : the methods, policies, and software used to prevent an artificial intelligence model from engaging in harmful actions (such as providing false information or exposing sensitive data)

Microsoft has built safety guardrails into Copilot that usually prevent the AI assistant from sending data to a bad actor.

—Matt Binder

… called the model a national security risk after being notified of a jailbreak, or a way to get around its internal guardrails.

—Hadras Gold

The general idea is to roll out AI tools with guardrails—that is, rules, policies and constraints.

—Thad Rueter

Synonyms of guardrail

• railing
• rail

Examples of guardrail in a Sentence

the car ran off the road, but fortunately only hit the guardrail

Recent Examples on the Web

Markey, a longtime progressive, and Moulton, who has carved out a moderate stance in Congress, are both calling for new guardrails on AI. — Garrett Downs, CNBC, 27 Aug. 2026

To get a full understanding of the agent capabilities, company engineers disabled safety guardrails that normally are in place to prevent the sort of hacks that eventually hit Hugging Face and one other undisclosed organization. — Dan Goodin, ArsTechnica, 27 Aug. 2026

Russian-speaking hackers used SpaceX’s Cursor AI agent to breach a Belgian chemical company and six other firms in recent months, in the latest instance of cybercriminals circumventing AI firms’ safety guardrails. — Brendan Ruberry, semafor.com, 27 Aug. 2026

Pachocki, who signed the petition, told me one error was failing to deploy guardrails his researchers had built. — Alex Heath, Time, 26 Aug. 2026

Word History

First Known Use

1860, in the meaning defined at sense 1

Rhymes for guardrail

• airmail
• assail
• avail
• bewail
• blackmail
• cattail
• cocktail
• curtail
• derail
• detail
• dovetail
• email

Kids Definition

guardrail

noun

guard·​rail ˈgär-ˌdrāl 

: a protective railing placed along dangerous areas (as of a road)