Source : Webster's Revised Unabridged Dictionary (1913)

Unreliable \Un`re*li"a*ble\, a.
   Not reliable; untrustworthy. See {Reliable}. --
   {Un`re*li"a*ble*ness}, n.

         Alcibiades . . . was too unsteady, and (according to
         Mr. Coleridge's coinage) ``unreliable;'' or perhaps, in
         more correct English, too ``unrelyuponable.'' --De
                                                  Quincey.

Source : WordNet®

unreliable
     adj 1: liable to be erroneous or misleading; "an undependable
            generalization" [syn: {undependable}]
     2: not to be trusted [syn: {undependable}]
     3: not worthy of reliance or trust; "in the early 1950s
        computers were large and expensive and unreliable"; "an
        undependable assistant" [syn: {undependable}] [ant: {reliable},
         {reliable}]
     4: dangerously unstable and unpredictable; "treacherous winding
        roads"; "an unreliable trestle" [syn: {treacherous}]
     5: lacking a sense of responsibility