untenable
un-TEN-uh-buladjMeaning impossible to defend, keep or hold on to
Memory hook un-TEN-able: TEN = hold, so it can’t be HELD. The sun is melting the snow fort, and Pip and Zoe can’t hold it much longer: their position is untenable.
With the river rising around the campsite, staying another night was untenable.
In context Once an older map turned up, the claim that the village was founded in 1850 became untenable, because the map, dated 1820, already showed the village.
Similar indefensible, unsound, unsupportable, insupportable
Opposite defensible, sound, tenable
From un- (not) + tenable, from French tenir (to hold), from Latin tenere.