WordWeb Online

1. Not worthy of reliance or trust
   "in the early 1950s computers were large and expensive and unreliable";
   - undependable, flakey [informal], flaky [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

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

Antonym: dependable

Encyclopedia: Unreliable