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

Officials from both sides have expressed skepticism about AI regulation in recent days, with Trump citing the need to stay ahead of China in AI development as a reason for avoiding guardrails. — Ashley Gold, semafor.com, 18 Sep. 2026

Expectations for a deal that establishes guardrails on AI are low on both sides, which continue to drive a headlong race toward potentially unfathomable intelligence capabilities. — Los Angeles Times, 17 Sep. 2026

Lawmakers in both parties agree more guardrails are needed, but even narrow attempts at regulation have fallen apart and a certain skepticism has set in. — Steven Sloan, Arkansas Online, 16 Sep. 2026

Board members and commenters noted at the board meeting, held at Polk State College, that the rules still allow AI tools deemed helpful to learning but provide necessary guardrails. — Austin Horn, Miami Herald, 16 Sep. 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)