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

California, home to the world’s largest tech companies, is placing more guardrails around social media and artificial intelligence as child safety concerns escalate. — Queenie Wong, Los Angeles Times, 10 Sep. 2026

Though there have been calls to increase safety guardrails on large language models, Anthropic’s approach sounds bizarre. — Joe Wilkins, Futurism, 10 Sep. 2026

As polls show the public increasingly favoring guardrails for AI safety — and opposing data center buildouts — the White House is likely to face still more calls for an explanation of why a more transparent framework is not possible. — Ashley Gold, semafor.com, 9 Sep. 2026

The agreement comes after New York City and Los Angeles both implemented one-year bans on AI tools for many students, giving the districts time to consider the proper use and guardrails. — Lauren Feiner, The Verge, 9 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)