Synonyms of inoperable

2 Syllables
fatal, serious, deadly, kerflooey
3 Syllables
terminal, cureless, nonviable, hopeless
4 Syllables
impossible, incurable, remediless, impractical, infeasible
5 Syllables
unnegotiable, immedicable, irremediable, irreparable, uncorrectable, unserviceable
6 Syllables
irrecoverable, unrecoverable, unbusinesslike