1. lacking a foundation; not based on a solid or secure base
2. lacking a factual or logical basis; without evidence or justification

Examples

• The accusation was foundationless and caused unnecessary harm to his reputation.
• Her fears about the project proved to be foundationless once the data was reviewed.
• The theory rested on foundationless assumptions that had never been tested.
• Without proper research, the argument remained foundationless and unconvincing.
• The rumor spread quickly despite being entirely foundationless.
• His concerns were foundationless; the company had an excellent safety record.