1.Definition: dangerously unstable and unpredictable

"An unreliable trestle"

Related Adjective(s):treacherous

2.Definition: lacking a sense of responsibility

3.Definition: liable to be erroneous or misleading

Related Adjective(s):undependable

4.Definition: not worthy of reliance or trust

"In the early 1950s computers were large and expensive and unreliable"

Related Adjective(s):undependable