WordWeb Online

1. Liable to be erroneous or misleading
   - undependable
    
2. Not worthy of reliance or trust
   "in the early 1950s computers were large and expensive and unreliable"
   - undependable
    
3. Dangerously unstable and unpredictable
   "an unreliable trestle"
   - treacherous
    
4. Lacking a sense of responsibility

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

Antonym: reliable

Encyclopedia: Unreliable