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

Meta immediately took out advertisements in major newspapers, pressuring its competitors to adopt similar guardrails. — Darius Tahir, CBS News, 8 Oct. 2026

During a Monday New York City Council hearing, representatives from OpenAI, Google, Meta and Anthropic were asked to assure under oath whether AI agents will always comply with safety guardrails to prevent catastrophic harm. — Staff, FOXNews.com, 8 Oct. 2026

Not only are those objectively terrible ideas, but chains of title put guardrails on what studios can do with many iconic characters. — Brent Lang, IndieWire, 7 Oct. 2026

Important-sounding acronyms are batted about to suggest internal guardrails — like MSI (Meaningful Social Interactions), CIT (Civic Integrity Team) or SATF (Soft Action Task Force). — David Rooney, HollywoodReporter, 7 Oct. 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)