1. Not worthy of reliance or trust
   "don't rely on my unreliable friend to do it for you";
   - undependable, flaky [informal], flakey [informal]
    
2. Liable to be erroneous or misleading
   "an unreliable generalization";
   - undependable
    
3. Dangerously unstable and unpredictable
   "an unreliable trestle";
   - treacherous
    
4. Lacking a sense of responsibility
   "The unreliable worker often failed to show up for his shifts"

See also: dangerous, erratic, fallible, irresponsible, temperamental, uncertain, unsafe, unsound, untrustworthy, untrusty

Antonym: reliable

Encyclopedia: Unreliable