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1. Likely to fail or make errors
   "everyone is fallible to some degree"
    
2. Wanting in moral strength, courage, or will; having the attributes of man as opposed to e.g. divine beings
   "I'm only a fallible human";
   - frail, imperfect, weak

See also: errant, erring, error-prone, human, undependable, unreliable, weak

Antonym: infallible

Encyclopedia: Fallible