1. impossible to bear or endure; intolerable
2. not able to be justified or defended with evidence or reasoning

Examples

• The heat in the desert became unsupportable by midday.
• His behavior toward his colleagues was unsupportable.
• The theory was based on unsupportable assumptions.
• She found the noise from construction unsupportable.
• The defendant’s alibi was completely unsupportable.
• Living conditions in the overcrowded shelter were unsupportable.
• His claims about the company’s profits proved unsupportable when audited.