“Robust” can mean physically strong, resilient, reliable, vigorous or well supported. Its opposite therefore changes with the sentence. These 13 words cover the main contrasts, from fragile objects to unreliable systems and tenuous arguments.
Quick List: 13 Antonyms
- Fragile
- Weak
- Frail
- Delicate
- Flimsy
- Brittle
- Vulnerable
- Unstable
- Feeble
- Insubstantial
- Unreliable
- Tenuous
- Faint
Fragile
Use fragile for something easily damaged or broken, especially objects, systems or arrangements with little resilience.
Example: The temporary structure was too fragile for heavy equipment.
Weak
Weak is the broadest opposite when strength, force, performance or support is lacking.
Example: The signal remained weak inside the concrete building.
Frail
Frail suggests physical delicacy or structural weakness and is often used for bodies, materials or arrangements.
Example: The frail frame bent under the additional load.
Delicate
Delicate contrasts with robust when something needs careful handling because it can be damaged easily.
Example: The instrument contains delicate components that require careful transport.
Flimsy
Flimsy describes something thin, poorly made or insufficiently strong for its purpose.
Example: The flimsy packaging tore before the parcel arrived.
Brittle
Brittle applies when a material is hard but liable to crack rather than flex under stress.
Example: The old plastic had become brittle with age.
Vulnerable
Vulnerable contrasts with robust when a person, system or process is exposed to harm, attack or failure.
Example: The unsupported server remained vulnerable to outages.
Unstable
Unstable fits systems, structures or conditions that cannot reliably maintain their state.
Example: The platform felt unstable on the uneven ground.
Feeble
Feeble describes markedly weak force, effort or physical strength and often carries a stronger negative tone.
Example: The engine produced only a feeble response when started.
Insubstantial
Insubstantial suits evidence, structures or arguments that lack enough material, weight or support.
Example: The claim rested on insubstantial evidence.
Unreliable
Unreliable is a strong contrast when robust means dependable under repeated use or changing conditions.
Example: The old connection was unreliable during peak demand.
Tenuous
Tenuous works for links, explanations or arguments that are weakly supported rather than physically fragile.
Example: The supposed connection between the events was tenuous.
Faint
Faint contrasts with robust when intensity, color, sound or signal strength is weak.
Example: Only a faint trace of the original pattern remained.
Match the Opposite to the Sense
A robust bridge, a robust computer system and a robust argument are strong in different ways. Choose an antonym that targets the relevant quality—physical durability, reliability, intensity or evidential support—rather than simply selecting a generic word for weakness.