Impossible to sack (expel from one's job). (adjective)
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Use "unsackable" in a sentence
"Well, well, well - it sounds as though Andrew Lansley's loose lips may have cost him his hitherto "unsackable" status."
"David Cameron defends Andy Coulson - but says no one is 'unsackable'"
"Recently the Mail published a devastating account by a whistleblower who revealed a culture of absenteeism, rampant inefficiency and 'unsackable' staff at the London council where he works as a senior planning officer."