Something, such as a position, excuse, or situation, that is described as untenable cannot be defended against attack or criticism.

// The scientists considered their colleague's theory to be bold but ultimately untenable.

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"According to The Economist, the disparity between investor enthusiasm about AI and reality might be untenable. They report that only 5% of U.S. businesses say they use AI in their products and services, and few AI start-ups are turning a profit. Most notably, OpenAI, the creator of ChatGPT, expects to lose around $5 billion this year because of huge outflows for employee salaries and the massive energy costs associated with running large language models (LLMs)." — Will Ebiefung, The Motley Fool, 25 Nov. 2024

Untenable and its opposite tenable come to us from the Old French verb tenir ("to hold, have possession of"), and ultimately from the Latin verb tenēre ("to hold, occupy, possess"). We tend to use untenable in situations where an idea or position is so off base that holding onto it is unjustified or inexcusable. One way to hold onto the meaning of untenable is to associate it with other tenēre descendants whose meanings are associated with "holding" or "holding onto." Tenacious ("holding fast") is one example. Others are contain, detain, sustain, maintain, and retain. Spanish speakers may also recognize tenēre as a predecessor of the commonplace verb tener, which retains the meaning of "to hold or possess."