That cannot be vanquished; undefeatable, inconquerable.(adjective)
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Use "unvanquishable" in a sentence
"Chelsea won the match, but the extremes of joy and sadness, hope and despair, were all wearing an Everton shirt – losers yet unvanquishable."
"As the group starts leaving, she has the unvanquishable impulse to erase the chalk scores."
"But Berdych will take heart: his form has been that of a contender and he is surely far more of a Goran Ivanisovic (finalist in 1992, 1994 and 1998; won it in 2001) than a Kevin Curran or a Cédric Pioline, both of whom also appeared, a little unexpectedly, on finals day opposite? albeit on wildly diverging career tangents? previous unvanquishable SW19 hall-of-famers."