What does "unreliable" mean?

Unreliable: 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.