hard-and-fast

adjective

ˌhärd-ᵊn-ˈfast 

: not to be modified or evaded : strict

a hard-and-fast rule

Synonyms of hard-and-fast

• certain
• stable
• final
• unchanging
• unchangeable
• fixed
• hard

Examples of hard-and-fast in a Sentence

hard-and-fast rules that governed the corporate environment in those days included strictures regarding office dress that were rigidly enforced

hard-and-fast beliefs that are the rock-solid foundation of their religion

Recent Examples on the Web

Dogs bred for alertness or reactivity may be more attuned to sound, though this isn’t a hard-and-fast rule. —Jamie Cuccinelli, Martha Stewart, 7 Apr. 2026

There are no hard-and-fast rules for replacing a mattress. —Sharon Brandwein, USA Today, 3 Apr. 2026

One hard-and-fast rule to live by in this case? —Stacia Datskovska, Footwear News, 26 Jan. 2026

But even in the absence of hard-and-fast rules and guardrails on how AI can be used in schools, education policymakers identified a number of ethical concerns raised by the technology’s spread, including student safety, data privacy and negative impacts on student learning. —Janice Mak, The Conversation, 22 Jan. 2026

Word History

First Known Use

1822, in the meaning defined above

Rhymes for hard-and-fast

• chloroplast
• epiblast
• opencast
• overcast
• protoplast
• rebroadcast
• telecast
• trophoblast
• ultrafast
• unsurpassed
• aghast
• amassed

Kids Definition

hard-and-fast

adjective

ˌhärd-ᵊn-ˈfast

: not to be changed : fixed

a hard-and-fast rule