Here are some ways to understand the word:
* In a debate or argument: If your position is untenable, it means you cannot logically defend it with evidence or reasoning. Your argument is weak and easily refuted.
* In a situation: If a situation is untenable, it means it's unsustainable. The conditions are too difficult or unfavorable to continue.
* In a position or role: If someone is in an untenable position, they are in a difficult spot that they cannot realistically continue in.
Examples:
* "The company's financial situation became untenable after the CEO's reckless decisions."
* "The government's policy is untenable in light of the recent scientific findings."
* "His arguments were so weak that his position quickly became untenable."
Think of it as something that's not able to stand on its own two feet.